I could see the entire first section of Ulduar being 10-boxable. FL, Razor, Ingis, and XT.

Past that - possibly, but its going to take some serious work.

ToC10 would be HARD - just due to all the stupid gimmicks. But its been dual-boxed, so things go up from there.

ICC? I could see the first "wing" 10boxable (Marrow, LadyD, Gunship, Surafang). (gunship would be loltastically intense and crazy). After that - I dunno - its stupid crazy after that.