So today I reached level 4 and was finally able to see how exactly all the ship equipment is classified. And honestly I think it could be better or at least I would have organized it a bit differently. For now we have equipment that is organized into tiers (t1-t4) with each tier slightly better, more expensive and incompatible with ships of other tier. Within tier we have different marks (I-III) (with note that MkIII items are only available to certain factions). Also certain equipment is (ship) class specific.
First thing I would change is to set a class restriction on weapons like there are for some modules. Same lasers that can be set on frigates shouldn’t fit on interceptors or fighters and vice versa. Why? It simply not fair that larger ships get more firepower for exactly the same price. Also it’s not credible… it not the same if you have 2, 4 or 6 turrets mounted on your ship. Frigate weapons of same tier should be like 10% more expensive than interceptor and 5% more expensive than fighter weapons imo.
Second thing is that equipment like weapons and all other modules should be backwards compatible for at least a tier or two imo. This means that i.e. t2 ship should be able to mount t1 equipment and weapons but t1 ships should not be able to mount newer t2 equipment. I see no harm to gameplay in this if someone chooses to use t1 equipment which is inferior (at least weapons which do less damage). Instead you are forced to buy completely new equipment from scratch to fully prepare your new ship for battle.
So to sum it up I suggest class restriction for ship weapons and backwards compatibility for equipment of lower tiers. This would be more credible than the system implemented right now and also it would spread out expenses more evenly than they are now. In my case I didn’t have anything new I wanted/needed to buy for quite some time and then suddenly (when I reached rank 4) I would have had expenses in over my head if wanted to buy 2 or 3 new ships of that tier and equip them fully since all the equipment I had at that moment became obsolete.