If we move to other games, I'd say only have innovative games, particularly unusual games, or non-mainstream games that should get tons of sales, but instead yet few.
Just to retain the atmosphere of Oddworld.
A lot of new themes would not be necessary: Change the Logo at the top, maybe add a different game character instead of the glukkon, someelse instead of the snoozer; then change a couple of the other graphics, such as the 'new posts' ones.
However, if we move into other games, we should still concentrate on specific games, with specific forums for those games, as so:
Zulag 1:
Oddworld Discussion
[Next Innovative Game] Discussion
[Next... Psychonauts seems popular here?} Discussion
Zulag 2:
There's no need for the spoiler or the help forum. No need to reduce the Fan area - simply make the Fan Corner encompass the new games too and keep the Non-Oddworld art/lit.
Maybe make Non-Oddworld Gaming a main forum in Zulag 2 (or indeed 1).
That's assuming we want to go down that route. Would it add spice? Would it actually work: Do we know enough about these other games, and are we as interested in them to discuss? The good thing about Oddworld is the Mythology. In normal games, you'd need Multiplayer to keep the discussion going on for so many years.