Assault logis already fill their spare slots with compact hives. This idea will make actual logis like my speed-hacker less viable.

The problem is that CCP will look at the situation and the thought pattern will probably go like this:

People are using the Logistics suit as an Assault Suit what should we do?
Nerf the Logistics Suit.

Instead of going, why are people using the Logistics suits over the Assault suits?
Slot Layout among other things.
Maybe the assault suits simply need to be more effective then?
Potentially, maybe give them something like oh idk, damage output increase for the assault skill instead of something that makes no sense like shield recharge?
Would be a good place to start.

So fear-mongering to get people to support your specific idea.

(Fix TTK first) give assaults 1% damage bonus per level as the general assault bonus. Doing more damage reinforces the role of the assault.
Give each assault bonuses to their specific race's weaponry. Minmatar could get explosive/projectile clip size, Amarr assault keeps laser bonus, Caldari could get more effective range for railgun weapons, etc.
Bam! now assaults are better at assaulting.

Give logi bonuses to equipment. General logi bonus should be PG/CPU reduction of equipment, and each logi could have an equipment related racial bonus.

More details here.

Logis would still have less speed, less stamina, less base shields (meaning depending on how you use the extra low slot, they may have less HP than assaults), and less shield recharge. Also having no sidearm is a pretty big deal if you're using a weapon like the plasma cannon, swarm launcher, laser rifle, or sniper rifle.

The only benefit a logi would have when assaulting is PG/CPU, and that extra low slot. Everything else would be better on assault suits when assaulting.

Logis would still be able to tank more, making them good at defense, but less agile, and bonuses would make them more geared towards equipment use.
Assaults would be more offense oriented with damage and weapon bonuses, and more agile, and versatile in combat because of sidearm.

We should have it so all suits get an invalid fitting if all slots aren't filled. While we're at it lets get rid of the standard suits fitting proto weaponry by leaving the 1 equipment and/or side arm slot empty.

This is a stupid idea, shot down multiple times in the past. Compact hives in every slot and BAM, no-one gives a damn. All it restricts are people attempting to make interesting suits.

Give it to scouts to give themselves an advantage over Assaults. Assaults don't need more than 1 EQ slot.

HI

WHAT IS THE LOWEST CPU/PG ITEM I CAN USE TO FILL MY EQ SLOTS WITH???

that why you make it so its only viable if 2/3 or 3/4 of their gear is equiv lvl to the suit they are running