SupCom FaF has a very long list of changes, I'd guess some of the people behind it already have access to source code. IMO only changes that are still missing is making it multi-threaded and maybe fixing some AI deficiencies such as pathing and the like.

The first would be great, but probably very difficult technically. The second would probably cause a holy war in the community, as multiplayer RTS enjoyers glorify fighting against the genre's jank as an expression of skill (admittedly it would completely change all micro).