Dynasector / Starsector both kind of already have this system in place for Nexerrelin, however the player has to do it themselves. I believe there's a text file somewhere in either of those mods you can edit that gives you faction whatever tech you want - the higher the number for that tech, the more 'weight' it has in your own faction, the more likely you're going to see that tech in your faction markets. So you can customize your faction to be, say, entirely Blackrock or entirely Diable, or perhaps you can do the whole 'every single time I conquer a market I add that amount of tech points from that faction to mine' thing.
The system you are proposing; I reckon it'd probably be a bit too difficult to engineer properly, especially when the player can kind of already do it manually kind of.
Forgive me if this is impossible, but would it be possible to use the NexerelinOptions.json file as the default weight, then apply modifiers to this based on what happens in the player's game?
The player wipes out a high level Tri-Tachyon fleet, gaining +0.05 weight towards TT. The player eliminates BRDY from the sector, causing their weight to fall a dramatic 0.5. The player reaches cooperative reputation with the Hegemony, and gains +0.2 weight.
This would need some tweaking to differentiate between purchasable ships, and ships that would spawn as part of the faction's fleet, but I'd like to say it could be done - but here's me with meagre programming skill, promising the heavens.