It's been a while since I've been around here and was considering discussing a new project on which I'm working. I noticed that the Indie Design forum is closed, but this forum seems to be similar in function. Would this be an appropriate place to discuss mechanics and other design elements? Thanks.

Yes.

The new forum structure is:
*Share the system you're working on in First Thoughts. Rough out mechanics, share concepts and premises, and get messy.
*Once you've got an "alpha game" worked out, take it to Playtesting. That's the refinement machine, and the place you want to get later feedback at.

If the game is in playtest and you're looking for feedback/re-tooling/troubleshooting/confirmation of something, then post your Actual Play(testing) in the Playtesting forum. Even if the game isn't yours, and you were an external playtester, post it here.

*If you've had a rockin' session of a published/finished game, share your experience in Actual Play.