The doctrine: don’t accept any default model upgrades. Reasoning: or else Tremulous will become second Unvanquished, and it will compete with Unvanquished for the player base, and both games will end up worse.
I’m assuming ‘model upgrades’ means 3D models in a new format, like IQM (Inter-Quake Model format, an opensource binary version of Doom 3’s MD5 model format, supporting skeletal animations). Tremulous can use IQM thanks to support in the ioquake3 engine (many quake* projects have switched to the format), and it makes sense that if new assets were introduced, they would take advantage of the best format for the job (much better than q3’s MD3, with its crappy vertex animations and crappy exporters).
This leaves the fact that if new assets were in fact made for use with the new GL2 renderer, Tremulous could look visually similar (or better) than Unvanquished, and assets (3D textures and models) produced could be utilized by other open source games.
This is incorrect. Tremulous was first, and Unvanquished has since moved away from it. Unvanquished is its own project and their goals (shiny new game written in a different language and under a different license) are independent of the goals for Tremulous (legacy support and fixing basic game-play issues).
The Unvanquished team does not care about getting the Tremulous player base to play Unv; so this statement:
…is totally WRONG. Besides, Tremulous has many more players (currently). Unvanquished will build their own player base in good time, and people are free to play any game they like.