Any thoughts about opensourcing the work/development? Code made available for everyone has so much more potential than just building another closed source project.
Have a look at Freespace2, Doom, Quake3, Open Morrowind, ScummVM and such - these codebases are available to a broad community which keeps these projects alive and improves them (ever thought about playing on a printer display? Well, you can do this with Doom because the sources are available).
Someone could work on a XWVM Linux executable right now and push the changes back to the mainstream codebase (but maybe Unity just spits out a compatible binary for every supported system, I don't know) or several people could divide the work to enable all game missions ASAP if there is documentation how to do it.
Most mods I know are kept closed source like the original game they use and in 10 years they share the same fate as the original game: no or decreased development, changed technologies, development- and reverse engineering knowledge gets lost and someone has to do it all over again from zero.
I reverse engineered TIE Fighter savegames and that cost so much time while all trainers and editors mentioned in the web were lost (just download XY from Geocities and ... oh wait, nevermind, it was shut down several years ago).
Currently your development team does all the work. I led a small team to develop a roleplaying game in our spare time and most developers always had other things to do (learning for university, girl friend, work, partying and whatnot). We developed closed source and we died after 2-3 years.
No need to convince me about open sourcing. I was convinced since the beginning.
The only problem is that we are making use of some libraries that don't allow for open sourcing, in particular, the input library, some backdrop assets, and the whole collection of model placeholders from XWAUP.
Until we find replacement for those, and it can take a while, we can only make public the code that concerns to the game logic and AI, but not the rest.
Since that would make the project not really easy to contribute to, it's better to leave the project private until later.
If there came the day that we cannot dedicate more time to this project, and in case we have not yet open sourced it, or got rid of the incompatible assets and libraries, we would just "rip them off" and make the rest public.
Regarding Linux, Unity just generates a Linux and Mac build with the toggle of a button, but we have some libraries that are, for now, Windows-only. In particular, the TrackIR integration library, because there doesn't seem to be one for Linux yet.