I'll be interested to see how people are writing in a few decades. I can't imagine that Unicode won't be almost exclusively used--with ASCII reserved for BIOSes and such (even now, we're getting close)--and surely most Americans will one day figure out how to do ©óól ßtúff wíþ ðeir kœybóárds. And I think the trend of niche groups and cult revivals will increase. So surely there will be small groups of people using interrobangs and þorns and umlauts (coöperate, anyone?), and if people are using it informally it'll show up on Facebook and blogs, and if it's on blogs it could spread to magazines and newspapers, and if it's in magazines and newspapers it could become acceptable for use at work and school. So who knows, maybe it'll become trendy again.