I'm curious why you guys would like that feature - is it just to make it easy to stay anonymous? If you're worried about that then until I have this feature you can give a fake/temporary email - I don't validate it, it's only used to email a link to reset your password in case you forget.
Are there other reasons? It's helpful as a developer to know why users want a certain feature, to make sure I give you what you want.
I own several websites where people can donate (no BTC for now). It would be a simple way for them to donate this way and add BTC donation at the same time.
More simple => more users.
You're right, that would be an extremely simple way to let your visitors donate BTC. It wouldn't really cost them anything, just a bit of CPU time.