Chances are that (pending feedback, and my own actual testing of them) I will use these fixes as much as possible. It'd be a shame to waste the effort that went into making them, after all. That being said, it's never a good idea to rely on the fiddlier details of an experimental release, even if it was one that came from me.
There's no final decision in regards to those things yet. If you feel it's important to prepare your levels now, I would say the best option would be to make them independant of the outcome on those. Be aware that the next update will end up being a pretty major one due to the large amount of physics changes / fixes, so it's to be expected that not all content will be upgraded to it right away. Due to that, and the removal of gimmicks etc, V1.43n-F will remain easily available, so there won't be so much pressure to upgrade as quickly as possible.