Honestly might not be such a bad idea. Unity is built on .Net, which Microsoft also owns. The teams could work together to get Unity modernized and cleaned up, and I bet developers would trust Microsoft more than Unity (Consider that Microsoft also owns VS Code, Github, npm and more that tons of devs frequently use)
MW2 had many iterations of fan servers. It started with alterIWnet, and ended with IW4X, which was recently shut down by Activision with a cease and desist. Fan modded versions of the game with dedicated servers and a server browser, with known security vulnerabilities like this one already patched out. Thanks to Activision, there's now no way to safely play this game anymore.