Well, one would hope that for situations when such proof of receipt is required, similar conditions (such as going in in person) would still apply, even if the original summons/documentation was sent electronically. That said, I think a friend of mine received a court summons in regular mail while overseas. Can't remember the details though. If that doesnt require registered mail, what does?
I agree normal mail has no proof of receipt, but the onus is still on you to check for it and to make ammends when you don't receive the mail. It's a lot more effort than being able to check mail from anywhere anytime.
Yes, with electronic message delivery the ability to check if someone actually received the communication can be designed in, but I don't see how that's a bad thing, unless you regularly use the excuse that you were on holiday to pay bills late?? Instant receipt doesn't necessarily mean that you have the ability to respond to whatever the government requires of you immediately (eg if you are on holiday) but at least you would be aware of it prior to not appearing in court or whatever (ok getting drastic with examples here but you get the point).
I like the idea because I hate snail mail and the point I was trying to make in my original reply is that it is no more secure or reliable, and the onus is still on the individual to check the mailbox, and electronic delivery doesn't really change that.
Segwaying... the only issue I have with the idea is that it lends itself to the requirement for a unique government ID for everyone.