We hadn't really thought about importing existing keyrings to be honest, but it seems like a good idea. I can't immediately think of any reasons why we wouldn't do it.
It would make me very very happy, if that's a good reason to do it. :-) The user experience with encrypted email frankly sucks right now, and if you improve it, I think you'll be getting a lot of existing GPG users as well as newbies. But we all have keys already...
Seems like a good enough reason to me ;) The only challenge I see is that those users will still have to change their email addresses (it's not a huge extra step, but we don't want to worry about custom domains out of the gate) and some public key servers make it difficult to remove the old one.
I'd sign up for a "$8/mo plus four invites" plan (i.e. keep it under $100/yr), but not without custom domains. I bought my own domain a decade+ ago for the exact reason that I never have to switch addresses again.
Hmm, interesting, thanks. I don't foresee custom domains being a big challenge, and it probably won't take too long for us to add support, but I would just want to make sure we stamped out the lion's share of bugs first.