We haven't set out a specific plan for ICC, as that is quite a way down the road.
How it will work with Naxx & Ulduar is like this.
Naxx 25 is available = you can donate for Naxx 10 gear. (That's right now, I believe.)
Ulduar is made available, let's assume it's all sizes&difficulties = Ulduar 25 & hard modes (do not confuse with heroic) are available = Ulduar 10 loot can be donated for.
ToC and ICC complicates things a bit, since both of those raids have 4 difficulty&size settings. Since we haven't set an specific plan for these just yet, I can't give you an exact statement on how it will be handled. That being said, I would expect that once ICC 25 heroic is available, you will be able to donate up to 264 ilvl, and then up to 271 ilvl once Ruby Sanctum 25 heroic is available.
Will everything be available for donations once all content is available? I cannot say, but probably not -- being limited to 271 ilvl at the highest.
Shadowmourne and Valanyr? As of our current design choice, they won't be donate-able -- quest chains only.
Of course, we're accepting feedback on the matter.
Aye, that can't be denied. But the real question is: Is it fair? Is it acceptable?