Well, we've gotten our hands on the level 85 rating conversions. It looks like you are going to need 268 crit rating per point of critical strike percentage.
Of course the numbers on all of your gear are going to inflate quite a bit: you'll have lots more critical strike rating at level 85 than you do now. Still, requiring about four times as much rating per point of critical strike is going to mean less critical strike, because your stats are not going to be four times what they are now.
We have seen that the new enchants need a level 300 item to work. This is from the alpha and could be way off, but level 300 is a pretty good prediction. Between vanilla and BC first tier raids we went from level 86 to level 115. Between BC and WotLK we went from 164 to 200. Top tier WotLK raids drop 277s, but we know things got a little out of hand in terms of item levels, so between 300 and 315 probably what we are looking at for item levels for first tier cataclysm raiding.
In first tier WotLK raiding we had about 2000 spell power, so an arcane mage derived around 55% of their damage from spell power and the remainder from base spells. A well-geared (not top-of-the-world guild but doing okay) mage these days has around 3500 spell power and 1000 crit and haste ratings. If we go from 264 to 300 gear we can expect about a 40% increase in our stats.
Let's look some numbers. Please bear with me through these loose estimates, the accuracy of the estimates will end up making very little difference to the conclusion. We will guess a level 85 mage with first tier raiding gear will have around 4900 spell power (pre-buffs) and around 1400 crit and haste ratings. Let's give them a 5% base crit and estimate 15% crit from talents and buffs. That would give them a total crit of around 25%. We'll use the first-tier WotLK value to estimate how much of their damage comes from spell power and how much comes from the base spell. And lets, for the sake of argument, say the mage does about 15000 dps (based on the fact that mages can do almost this much right now and that damage between the end of BC and the beginning of WotLK remained pretty similar after as rating deflation cancelled out increased spell power).
With all this, 1 spell power would increase the mages' dps by around 1.7. Arcane mages crit for 1.75 times the base spell, so how much would 1 crit rating increase their damage. Well, one crit rating would increase their crit chance by just under 0.0039%. That means instead of doing 75% extra damage 25% of the time, they do 75% extra damage 25.0039% of the time. 75% of their damage is 11250, and they do it (1.250039/1.25) - 1 = 0.00312% of the time. That's 0.351 dps. That makes crit rating worth about 20% of a spell power.
Now spell power won't be on items, and we don't know exactly how you will get it, whether it will come 1:1 from int or at some other ratio, but it is pretty reasonable to expect that we won't have a great deal less spell power at 85 than we do at 80, so we are going to need to get it at roughly the same levels as we do today. At worst I can imagine a 1:1 ratio from int, meaning that spell power would be slightly more expensive item point wise than it is right now. Even if it is 1:1 (rather than it's current .85:1) that would mean having a stat that is at least 5 times as good as another for doing damage. Of course mages might have talents that increase the amount they crit for or proc off crits in other ways. But in order to make spell power and crit even out they would need to crit for the equivalent of five and a half times their normal damage.
Blizzard has recognized that it creates problems when one stat is so much more powerful than another, and I'll be very interested to see how they get around this.
The most your crit can get to is 100%, and they really don't want it to get anywhere near that high. You have a base amount and you have buffs and talents, so your crit probably ends up being 20%-ish before you get any crit rating at all. With over half your damage coming from spell power (and arcane mages actually have a pretty low ratio here, with 2000 spell power fireball is well over two-thirds spell power and Mind Flay is three-quarters spell power) you can expect your damage to increase by 30%-ish over the course of the expansion based on spell power increases (this would equate to a 60% increase in spell power). Suppose you start the expansion with 20% crit from base/talents/buffs and 5% from rating. In order to increase your damage by 30-40% from crit rating you would need to go from 25% crit to 62.5% if you crit for double. Since you started with 5% crit from rating, that means increasing your crit rating by 8 and a half times. Even if you crit for triple you would need to increase your crit rating by four and a half times to achieve that kind of damage increase.
How much would you need to crit for before a 60% increase in your initial critical strike rating would result in a 30% increase in damage? Fifty times! That's right, with a crit of 20%, 5% of which is from rating and 20% of which is from talents, assuming that a 1% increase in spell power is equivalent to a 0.5% increase in damage, it would require that you crit for 50 times normal damage for you to value a 1% increase in spell power the same as a 1% increase in crit rating.
What kind of solutions could there be? There are two breeds of solutions to this problem, I think. One is to take steps to equalize the stats, the other is to make it not matter as much that stats are so different in value.
In order to equalize the values of stats, they need to pound base crit value into the floor. Every point of base crit value has a debilitating effect on crit rating. There is the minor effect of reducing the actual effectiveness of each point of crit percentage you get (it means less as a percentage of your total damage to move from 150% to 151% than it does to move from 120% to 121%). But more importantly each point of base crit value eats into the cap they eventually want you to get to. If they envision you getting to 30% crit and you start with 20% then all the crit rating you ever get in the expansion can only give you 10% crit. If they envision you getting to 30% crit and you start with 10% then they can halve the crit rating conversion, doubling its power relative to spell power. Another thing they can do is make base spells account for much more of our damage so that spell power doesn't improve damage as much as it does now.
In order to make the extreme difference in stat values not matter so much, they can make it so we cannot gem or enchant our favourite stats. I've talked about why gems don't work in practice before. If one stat is even 50% better than the alternatives then the odds you gem anything but that stat get pretty low. If one stat is five times better than the alternative then obviously you gem nothing but that. If they don't let us gem or enchant Strength, Agility or Intellect then the fact that those three stats are far and away better than the others won't matter as much. They already put the exact same amounts of these stats on every item piece of the same level anyway because they can't condone any variation in their values, why allow gems to vary their values? If you couldn't it would mean that items with gems slots would be more customizable instead of just more powerful. They could also change the way they do itemization to make the primary stats more expensive in item points to reflect their power.
I would actually like to see a mix of these approaches. Having one stat be five times as good as another is a real mess for the game. To be honest, this problem seems pretty easy to predict and I will be interested to see exactly how bad things are in the beta and how bad they are when cataclysm actually ships. The biggest problem may ultimately be that if this is not addressed from the outset it will be almost impossible to address it mid-expansion and we might go through and entire expansion with nearly every class having only one stat that matters.
On the bright side, I guess that would solve the tank damage scaling problems.