Be cool if ships looked less advanced like the picture and a space station would be like the pre-ftl civ in early space age (like the ISS) just to give it an even more earlier feel

Separate mod - Recode armies such that honorbound warriors personality and related civics can recruit primitive armies (easy) and only invades with matching tech level armies (hard)

Player only mod. Event popup when transport enters orbit on primitive planet. Proceed as is, or option for each primitive age. Options destroy transports and spawn new ones with selected primitive armies on them.

Compatibility reference
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=854713844

Reference link: what can and can't be overwritten and how to do it - compatibility guide

https://forum.paradoxplaza.com/forum/index.php?threads/object-types-that-can-be-replaced-in-separate-files.990537/

Separate mod - Biowarfare as a special bombardment type that triggers plague events and kills pops, clinic and hospitals help mitigate plague. Techs for bioweapons vs each species class? Special project for bioweapon versus each species?

Separate mod - Unity for internal affairs, Influence for external affairs. Consider edict to swap between them, but unity cost for influence points needs to scale like tradition cost does.

Dropship/Jumpship/ Highliner / Carrier FTL based on range restriction and range buff aura module for Rayki's Dune mod

Equal footing - give player 1/2 ship maintenance and pop living standard cost like AI gets

Surface to space missiles - fortresses event spawn an old style defense station armed with missiles

BFR planet killer - asteroid ship class, look at the Belt and at observation.2 Small one for tomb world, large for cracker effect.

Military power fix mod - revive?