This would probably require a lot of dev time to implement - but totally worth it!
Regarding the "Oh what would that even bring, people would still just solo":
If you now have on each server 300 people soloing and 50 people questing (spread among 28 levels) then it is pretty hard to fill lfms (especially outside main US game time) - if you combine 3 of these servers into one then you have 900 people soloing and 150 people questing (again, spread among 28 levels) => that's far more people to fill up an lfm. .... So: No, I don't think that the majority of people would change their play style (some would) - but those that want to group would have far better chances to get into a group (and newbies would not so much be presented with the ghost town lower levels can be - especially outside main US gametime).