I definitely stopped writing for a few days, and definitely got yelled at by a lot of people. >_> <_< Less that, more text. HURRRRRR
So, raids. Presently, raids are 10 or 25 people. The "or" is the difficult part there. You see, fight complexity does not change between 10m and 25m versions. I realize that I'm using the same 2-3 fights for every single example here, but I'm going to have to go back to them AGAIN, simply because there's not a lot of content yet. WTB Ulduar. Anyway take... *drumroll please* Sartharion! With 3 drakes up, Sartharion requires three tanks. One tank must be on Sartharion himself, one tank must be on Drakes, and one tank must be on Adds, encompassing both fire elementals and whelplings. The issue is that 10-man Sartharion requires the SAME number of tanks, in the same roles. Yes, I know it's possible to do 10m with 2 tanks and a warlock, or in incredibly overgeared situations, there have been reports of the drake tank picking up adds as well, but in the vast majority of situations, 25+3 takes 3 tanks, and 10+3 takes 3 tanks.
Now, healing requirements fluctuate. I'm not going to lie, I don't know precisely how many healers are working various roles, but in general 25m takes 6-7 healers, and 10m takes 3 healers. Filling in the remainders, we're looking at roughly:
3 tanks (12%)
7 healers (28%)
15 DPS (60%)
3 tanks (30%)
3 healers (30%)
4 DPS (40%)
See the problem?
If you wanted to make two 10m groups out of your 25m raid, you're going to need some DPS or maybe ONE healer to swap over to tanking. Healing remains relatively static, though when you reach the point that you only need 5-6 healers (A huge issue, that I'll deal with another time...) the disparity shows up there as well.
This has been a big problem with my current raid group. We don't have a lot of spare players laying around, and while we have players with a lot of offset gear, most people don't want to spend time learning their offspec purely to attempt one of the most difficult fights in the game. Thus, each week, 25 of us can do S25+3, but only 10 of us can do S10+3, because the other 15 people, despite their skill, desperately lacks tanks.
Don't get me wrong, this situation isn't common. However, it's generally uncommon because 25-man fights require one or two tanks and 10-man fights also require one or two tanks, not because the tanking requirement is scaled down for 10m versions. I completely expect to see fights requiring 3 tanks in 25m Ulduar still require 3 tanks in 10m Ulduar, leading to the exact same situation repeating. I do feel that if a fight requires 4 tanks in 25m, it will be scaled back to allow less than 4 tanks in 10m.
The question is how to balance 10m raids to require reduced numbers of tanks without changing the difficulty of the fight. However, I feel that it's doable. For example in Sartharion, if you're attempting +Drakes, you could either remove adds from the fight but increase the HP and damage of drakes to compensate for the lack of adds, or you could have adds gain threat based off the drakes so that the drake tank is holding adds and drakes, but slightly decrease the damage output of adds (so that it's survivable). I'm sure there are other viable solutions as well.
Requiring the same number of tanks in 10m runs as 25m runs is a dangerous precedent.