We do not have built-in support for aircraft dynamics. Vehicle physics are currently not support, although this is something I want to add in ASAP. I have some code that produces really nice results, but I just need to spend a month or so integrating it.
Moving between different versions is a challenge in any engine, but I can definitely say our API and system is a lot more stable than what I have seen in Unreal. There will be some major shader changes in Leadwerks 5.1, but this will only affect custom shaders. For everyone else, the update will be seamless, as long as they just update the project with the latest shader files.