[chrisweekly]

I let go of my initial preference for SASS over LESS when I started working with TBS2, and continue to enjoy working with LESS. On general principles I'd recommend using the official LESS version.

Yes, LESS is actively developed and (incrementally) changing: https://github.com/less/less.js

As for Bootstrap, I have no insider information, but would be very surprised if they abruptly switched.

On the contrary: last year when I asked @mdo and @fat if Bootstrap would ever go mobile-first (vs the horrible mid-sized-first-and-scale-in-both–directions approach from TBS2), I got a flat "no" in response. [groan] So I have no idea what those guys might do in the future. But for them to switch doesn't seem likely to me.

FWIW My current project is using TBS3; so far, so good.