It is possible. There are tools for capturing network traffic, and with enough dedication and time, one could reverse-engineer the protocol. Building a server after that is more of a traditional exercise in writing a networking service backed by a database, etc. Nothing too challenging, in other words. But the reversing step is the difficult one - mostly because it's a trial and error route, so you make little by little progress, until you have the protocol figured out. With many false turns and backtracking. It's an art in itself to some extent, really.
Certain knowledge of network programming is required. A bit of experience with packet filtering, also being able to use a debugger (like x64dbg) helps too. But more than anything, somebody must really really want to do it, in order to be successful in this task. ( If you were to ask me, then sadly i have no appetite for this work )
I'm quoting you just to see if anything has changed from your side. I'm pretty sure many people would try to help you if you could just give it a try and assign simple tasks to less experienced developers (us). You don't own to anyone but you're one of the few persons that could help save this game and realistic virtual football as a whole. Nobody trusts the companies anymore, they have proved that they don't care about our experience or enjoyment, unfortunately they only care about our money, which is fine if we could at least get a decent product. But we don't and it doesn't seem that this could change anytime soon.
May you please at least consider this? Most of us could probably do basic packet sniffing or write basic methods/functions and generally contribute in a shared git repo.