I think it could go either way, honestly. As far as modern efficient e-mailing goes, it will simply be nice in many ways to have floating apps in the room instead of windows on a monitor, once the comfort/productivity tradeoff improves. But also, maybe when I open a real letter, my glasses recognize it as a letter, scan it into my library and blow it up into a floating virtual page, with or without OCR, maybe with additional context and history. Maybe I can choose to open a UI to respond digitally, or maybe it physically points me to my paper and pen. I can do any combination of writing a real letter or a virtual letter and sending it digitally or using the oldfashionedletters.com plugin to send out 100 cursive wedding invitations supported by whatever digital back-end is activated when the recipients' glasses detect reception of the letter. Point is, there's a unification of both approaches and they each gain new superpowers.
You're talking about novelty wearing off, but I think that might just be the difference between good and bad skeuomorphic design. Your email scenario is definitely a plausible thing that someone would make right now, and it would absolutely suck and die, but maybe it's just part of an experimental trend that will exhaust itself like that period in the 90s when every new cd-rom you'd pop in would autolaunch a unique, horrendously ugly and confusingly skinned UI that looked like it was straight out of a Cronenberg movie. It suddenly becomes easy to make a bunch of dumb shit and it takes time to see what sticks, and there's a lot of silliness on the road to best practices... but they ARE buried somewhere in there, we DO eventually get to a fundamentally better way of interacting with computers.