Isn't one reason we don't have transparent support for bigger pages that huge pages are just too huge? It's 4mb on x86 iirc. Why don't they support something like 64k, 512k as well as the really large ones? Surely that would make it much easier to use bigger pages transparently. Apps probably still need to give hints to be able to use the really really big pages.
As I understand it, POWER cpus do have a range of sensible sizes as well as the massive pages. AIX (I think) support the smaller ones transparently and the big ones explicitly. Seems quite reasonable.