There is a mod called "space platform, for ground", its purely aesthetic, but it would be nice if it gave more productivity and speed, but no resistance bonus, maybe even a penalty in resistance.
I think its a great idea to help in the early stages of the game with some extra speed without using shit ton of resources on modules.

I could add a custom tier separate of those of the originals since adding another one along the existing 3 will take a bit of rearranging existing ones

Its not exactly a higher tier, its one focused on production instead of everything...
Im using your mod for a few days now, and the extra resistance on walls and turrets really helps a lot against Rampant Fixed.
The small productivity bonus its a bit of a pain with ratios in the factory, but overhaul, I really like your mod, its not overcomplicated or overpowered.