Your question isn't bad, but it deserves a huge explanation why it will never happen:
1. What makes you think that it would be stopped maintained one day? I release patches every month, and the first one was already released in 2011: viewtopic.php?t=1070
There is no other Unofficial Patch that received so many updates over years, so this argument is somehow exaggerated.
2. Even if the maintenance stopped one day, the existing installers (and perhaps Multiplayer too) would be still available / running with the older version. There are fan-patches which weren't updated for years, and still people enjoy them.
3. Game-modded stuff can already be viewed, since most of things are based on text-a-like .ddf files.
Now explanation why it won't be released public:
1. There is a risk that the Launcher would be compiled by third-party, malicious code injected and then fully used for monetization.
2. It's a project that was worked on for several years, including when I was 14 years old. It just looks bad and making it public would not help. Idiot people (which do it even now on the Support chat) would only give negative comments like: "how bad it is" or "you should make it better". But their contribution would be 0 until they needed to use it for their own profit.
3. Sharing the source code of the launcher / multiplayer would be dangerous for the security of it. There are functions for Administrator permissions at the Lobby, code that prevents unauthorized users to use "Dr.MonaLisa" nickname, security that prevents players access the lobby using third-party software, etc. If someone had an access to see how those "blocks" are done, then would only use it for attacks on EE2.eu, not to make any help.
4. It would cause a risk, where (already not so active) multiplayer would be split on multiple other servers, just because someone with "admin aspirations" would want to have full control over things and in general avoid fair-player rules posted at this forum.
5. There are game glitches / cheats which were present in the official version of EE2, and fixed with Unofficial Patch 1.5 (for example resources glitch). Sharing any information how they're blocked would be a gift for cheaters who only would use the source code to bypass those fixes and cheat in game.
6. Even MonaNAT ( https://www.ee2.eu/multiplayer/help/#monanat
), which routes traffic between players on MP, with few details could be used by hackers as a "free VPN" service, or to generate extra traffic.
When you look at it from my point of view - you can see that sharing the "source code" could be the actual end of EE2.eu. I wouldn't have time to focus on things like better, encrypted authorization methods, dealing with hackers who just were "invited" by receiving all necessary sources, etc. All the future work would then be focused on fixing the existing things, just because some clown criticized the existing function or made a pull request on github with a "better looking code" which works exactly the same way as my original. Not to mention that the whole UP1.5 Launcher is in a single .cpp file with 48300+ lines of code. It all would be very stressful for me and I won't put myself on risk of getting even more demotivated.
And at the very end: In this community it's hard to even get players to test things. For the Language Changer files we've been waiting for several years and still I have found most of them myself. I don't believe there would be any contribution in the Launcher / Multiplayer development. It would only be used by people who want to see how some function works like and copy it over to their own projects. This isn't going to happen, especially because I have bad experiences with sharing sources (for my other project) in the past.