Next Vu Is...

The champion wiki has a list of confirmed VU slates, with references of course. Twitch and Singed are both on there, WW is slated for both Kit Rework and VU, and Sion will have a complete relaunch (AD is more likely apparently), though I think their actual release time will depend on the Rioter's progress with the champion.

ex. Rather than releasing whoever needed it most next, they might release the Ryze VU since his model has been confirmed to have already been finished.

http://leagueoflegends.wikia.com/wiki/Champion

EDIT: They just announced Twitch's VU heading to PBE. OP called it. ^^ http://www.surrenderat20.net/2014/04/champion-update-new-breed-of-plague-rat.html#more

Most likely not. Sion & Warwick are more likely candidates.

EDIT: Twitch VU was announced today.

http://na.leagueoflegends.com/en/page/champion-update-new-breed-plague-rat

Sorry didn't know it was announced but I linked it for you guys. guess I was right

They actually do have a singed VU ready, I think.

A rioteer showing Heimerdinger's VU before it was out also showed a singed one. He said it wasn't in stone though, they may make some changes.