We had this argument on the Darktide forums about Java. I can funnel time into the project to help, but using Java and C# for everything is not a good idea and could be a huge waste of time. The big reason why games, especially heavy server side games are written in C++, is lag and java's shitty garbage collection. You can argue that its fixed all you want, but there have been very few games written in Java that are mainstream games, and UO costs next to nothing in server side management/client resources, which is a big reason why Java works for it as an emulator, and the game is very basic in terms of combat animations, etc. AC is very heavy on the CPU.
The other big issue as someone stated, if you write it in Java/C#, you will most likely never get the animations to work the same if you start from scratch.
Anyways, I code Java, C#, C, C++, and Assembly (among other things) all day. So I can help out with whatever needs done.