Discourse is a big inspiration for some of the features going into our redesign. :]
Unfortunately, we're still using a PHP backend with mostly static front end pages occasionally fluffed with JS. Discourse's front end is built on an awesome framework called Ember.js, which is 100% JS and lets you have that full-page "app" kind of experience.
I actually originally wanted to do a similar thing for PC, but at the time Steve wasn't a fan and wanted to keep static pages (for a lot of reasons). So we started writing PC 2.0 with retro static pages. Buuuuut I've slowly warmed Steve up to the idea and I built a proof of concept that will hopefully push him over the edge, so you can maybe expect a Javascripty fancy app-feel for PC 3.0. ;]
Either way, our 2.0 redesign is way, way better than this current vBulletin mess. It's served us well over the years but you're right, it has absolutely shown its age and it's time to retire it. Once our redesign is out, not a single part of this forum will resemble vB. You won't even be able to tell some of the code still runs it.