After some discussion, I looked through a lot of images of loadouts people posted on the Discord and saw that easily >90% of the s-mods used were some variation of:
Safety Overrides
Augmented Drive Field
Heavy Armor
Expanded Missile Racks
Hardened Shields
Integrated Targeting Unit
Occasionally I'd see Hardened Subsystems for some SO/Phase ships, and rarer still I saw Militarized Subsystems along with some built-in Reinforced Bulkheads and Blast Doors for Derelict Contingent ships.
Overall, there's a rather boring lack of diversity when it comes to placing s-mods on your ship, since it's basically always a no-brainer to include 2-3 of the six hullmods above. There's already been discussion about building in Safety Overrides, but I'd argue that this could reasonably extend to the other ones listed as well.
My proposal:
Remove s-modding non-logistics hullmods above a 5/10/15/20 OP cost. The image below shows which hullmods would be applicable under this rule (highlighted in green):
(This was a bit of a lazy screenshot, but it's sorted by OP Cost so everything above Unstable Injector would be disallowed except for Augmented Drive Field. Operations Center and Militarized Subsystems should also probably be whitelisted.)
There are a lot of good, interesting choices you can select within this subset of the hullmods, yet none of them are so much better or universal than the others as to be auto-includes the same way Hardened Shields and ITU generally are. This lets s-mods be a way to allow you some additional utility in your loadouts without being a simply thoughtless influx of OP.