I wanted to try some Hardcore in exotic Buffet worlds, but I read there is some issues with Stronghold generation in certain biomes. Apart from Ocean and Beach biomes, which have been reported already, I tried the following biomes when creating the Buffet world:
End Barrens, End Highlands, End Midlands, Nether, The End, The Void
None of those generated with Strongholds. I think it is an issue because it limits the enjoyability of playing these worlds in Survival/Hardcore mode, removing the goal of "finishing the game" and killing the Ender Dragon.