The rights to Tribes have been sold by GarageGames (which is going out of business) to Hi-Rez Studios. This company intends to create an MMOFPS based on the Tribes games, and the game will be called Tribes Universe.
An alpha version of the game available to a small number of testers is expected in early 2011.
The new owners of the series have a forum here: http://forum.tribesuniverse.com/forum/index.php
So, it looks like PlayTribes will never happen, and that leaked beta is all we will ever see of it.
Tribes MMO
Moderator: Sonikku