I think having more "subreddits" would be worthwhile - many times I've had something I'd like to discuss with LWers but not posted it because it was too off-topic. However, as others have pointed out, this has been suggested many times but not done.

Perhaps if we can find out how much money it would take for Trike Apps to be willing to make this (or any other popular) change, and it was a reasonable amount, we could arrange a Kickstarter or similar to see if we could get enough funds.