My starting point is that at some point in history, the IlKhan manages to push the Clans towards a real war economy.
This means that all the factories in Clan space will focus on a "few" designs that are all Omni, in order to maximise their efficiency and flexibility. After all, who needs 3 designs when you have one that can do the job?
To illustrate my idea, I will focus for now only on BattleMechs but feel free to elaborate on Vehicles and Aerospace Fighters.
Let's say that for each class, only 3 different designs exist and that all factories must focus on these 12 designs, depending on what they can build, they will build one or several of these BattleMechs.
All the production is gathered and split in 20 (for the original Clans) with each Clan becoming 1/20th.
For what remains, competition is open through Trials.
This will not endanger the biggest Touman as the existing BattleMechs are kept and are either replaced after loses in combat or dropped to Second Line units once the new standardised 'Mechs become more available.
This could in a few years create a bigger pool of resources thanks to the experience in building these 'Mechs.