The hard thing about multiplayer does not have much to do with the language used. Java is just fine for that. The problem with multiplayer is synchronization. You've got two (or more) simulations running on different machines on different sides of the planet, and you have to make sure they are in exactly the same state. The wiring needed for that goes through the entire program and is not something that is easy to add afterwards. Especially for a game where quick response is important.
Synchronization is not a problem, when peer to peer multiplayer used.
And as far as my knowledge in programming language goes (and it goes far), implementing multiplayer in Java or C# written software is much easier then doing it with C, C++, Python, ASM, etc.
Anyway lets give Alex to focus on finishing Starfarer. And when it will be finished completely, Alex will understand that something is definitely missing in Starfarer's main menu