3.6.10 is coming around the May timeframe, so it's not far off. The main point of it is to get in the changes which we couldn't get in for 3.6.9, but were originally slated for it. And of course, it will get additional bug fixes and performance improvements.
The scripting code in unstable is still getting changes, so until it's fully stabilized there isn't even anything to discuss. Until the API is solid and stable there is no way that it will be considered for a stable build, period. And even if it was totally solid now there isn't really enough time to get it bug tested enough before 3.6.10 comes out. The new code throws out compiler errors and has platform related code issues like crazy and there simply isn't time to fix/test it all.
We maintain two trees for a reason, stable code is for releases, unstable isn't. Some things will get added to both stable and unstable, other things won't. Anything in unstable is slated for 3.7 releases, nothing else. The stable branch will be for 3.6 releases, which will mostly be bug fix related. The stable branch is still getting new code and features, but nothing big so that we can actually keep it stable. If you rely on features and changes in the unstable branch then you have to understand that those things are not going to end up in stable, official, builds for many many months.
If you want those features then use an unstable build, and deal with all of the bugs that go with it. I'm not going to be using the unstable branch until later this year, and anything that I do work on will be my own stuff, I'm not fixing any more bugs in unstable until next year at the earliest (unless the bug is also in the stable branch). I'm only working on my own new features from now on.
If you want a stable and official build then stick with what we release from the 3.6.9 branch. It's fully supported and has the full weight of all bug fixing ability focused on it.