Does or Will Unity 5 open up...

Unity Engine
1

the mechanism FSM as a reusable component in code?
the job/threading system to scripts/code added by developers?

2

So Yes Unity Blog

And the job/threading system to scripts/code added by developers?

3

No, that’s for making it easier for Unity to make certain engine features multi-threaded. It’s not for end-users. You can already use .NET threads to make your own code multi-threaded, where it makes sense (and doesn’t use the Unity API).

–Eric