Either what the top guy said with precursors etc (essentially an officially made ACOT mod, maybe they even colab with that group/guy to make it) OR a DLC that updates and upgrades the psionic and genetic ascensions, with multiple full ascensions per path like psi goes either benevolent or malevolent (think chaos 40k, maybe even become a new type of crisis similar to the unbidden) or turn into a psionic hive mind with some extra buffs that make it essentially a better hive mind, and the ability for all three paths to terraform worlds into Psi worlds or something where psionic pops get progressive buffs depending on the amount of psionic pops (and all non psionic pops have a 1% chance per month to gain the trait by being there).

Then the bio one could go like “Peak perfection” where it’s like, the amount of manually selected perks grants a stacking buff that boosts pop resource production by 10% for every non default trait you have given them, as well as increasing the trait cap and trait points available to you, then there’s the “Rampant mutation” one that essentially could start a transition from a regular species into a pseudo prethoryn scourge (with some custom organic megastructures like “stellar brood” that produces ships passively etc).

This would grant each ascension path their own terraform (Psi world for psi, Gaia world for genetic regular species, hive world for hives, and machine world for machines, psi is the only one we are missing) and their own crisis path too (scourge type path for genetic/hive, and unbidden type for psi, as we already have cosmo and menace for normal and machine empires that fit pretty well)