Does Unity5 support .NET Framework 4.5? Is it still using the same Mono compiler than v4.6.x and lower? If .NET Framework is not suported, any plans to support it in the near future?
There are plans to support it in the very distant future after IL2CPP gets finished and is stable and gets ported to all other twenty or so platforms, but personally I think by that time we will be living in a world controlled by superintelligent robots that have enslaved humanity, so I don't think we'll be that concerned with game development.
Thanks @Eric5h5 for the link. It's a real pity, because even if we don't get current features of .NET Framework 4.5 it would have been nice if they used the newest Mono compiler, to avoid nasty IL compilation exceptions.
Unity has a heavily modified version of Mono to maintain compatibility across all the different platforms they support. This means it's not a simple thing to upgrade the Mono version. I believe at Unite last year they said not to expect a Mono version upgrade until IL2CPP is implemented across the board. Which will probably be late in the 5.X cycle or Unity 6.
I'm not sure it's particularly modified; the reason for not upgrading is because of licensing on some platforms (iOS). IL2CPP allows Unity to bypass that issue since it's no longer using Mono in a build. --Eric