So, something that you're getting a lot of negative feedback on elsewhere comes from the fact that a mod like this should really operate on a
whitelist, rather than a
blacklist, and that the list should be a separate file in config for ease of use by other modders to keep track of the data.
The real problem here is that many mods have "factions" that are more mechanical expressions than actual proper factions. Trying to account for every single one of these would be a nightmare and you'd have to try and keep up with it forever as new mods and ideas come out. Instead, it makes a lot more sense to make what factions get allowed a "whitelist", a list where the mission (and missions to come?) pull
only from the factions listed, which for vanilla should probably be limited to hegemony, luddic_church, persean, luddic_path, tritachyon, sindrian_diktat (with no lions_guard, they stay home!), pirates, mercenary, and remnants if you want to be spicy. Doing it this way will mean that users will have to add mod factions they want to see appear in the mission, but it will also prevent strangeness like HMI superbosses appearing in the fleets and making people annoyed.
Anyway, this is still a neat mod concept and not something many people try to do! Keep at it, IMO, it just needs a little refinement in its approach.