Yeah....in 3e, we're probably going to cut the Cant, at least from the rulespeak.
The quotes will probably still have it, but I see it more as a Sigil-only thing. And since Sigil has an overinflated sense of self-importance, many people from or influenced by Sigil have settled the planes.
After all, those on the lower planes probably have an Infernal accent, those on the upper planes probably have a Celestial accent....etc....
It'd be interesting to see a "Slang Common" for different regions of the planes, methinks....
Anyhoo, yeah. Certainly, the accent will be toned down quite a bit. It's one of the things most universally hated about PS, I think, even though I think it's cool. ^_^