Of course they should, think of all the possibilities. We could have the standard Ferguson Toilet, the king of bowls, if not even the Stradivarius of toilets!. It would have to be installed with the required plumbing. Next to it there could be a chemical toilet, with no pluming required, for the exploration runs or deep mining trips when we can not reach the Ferguson in time.
Of course then we also could have fertiliser double the value of normal bonemeal, heck why not giving it the credit it deserves and make it ten times as good as the standard bonemeal. Who doesn't want to have those power carrots or potatoes fertilised with this special ingredient.
This would be the first sensible addition Mojang has added since rotten flesh.
I say go for it. Better directly in the next release instead of having us wait for much longer, I could not bear the suspense!!!