V6 just has to overcome the major issues with players who remain on V5.
1. Performance needs to be better.
2. Playerlist needs to be feel and look like V5.
3. GUIs need to be adjusted for the new font rendering. It's kind of ridiculous it wasn't changed to emulate Windows V5's look.
If V6 doesn't meet the above criteria players are just going to be pissed off about the new client because it doesn't really offer players anything.