i like it, but it would be more CPU stressing for the PC/Servers...
imagine, loading the nether/overworld together into one chunk, including the mobs.
how would we prevent the Ghasts finding their way to the overworld? (making them unable to pas throu obsidian?)
the suits, sounds good. exploring there un protected kills you, duo to heat and lack of air..
only the lack of air - air is everywhere, deeper into the ground air pressure is higher then on the surface duo to...(click the link inserted in the spoiler)
so the protection suit would protect against extreme air pressure's
Display Spoiler
but i must say, i think this alters base files of mc, and thus wil not be coded by alblaka becouse he doesnt want to edit these sensetive files....
the overal idea if fantastic! but i doubt it wil be implemented...