I have an idea

It is possible to make the NPC who can give you a skills for weapons & armor? Or make Socket/Gems item with skills, which can be paired for weapons and armor. To upgrade your weapons & armor more further, this might be a good idea.

Divided into two types of upgrades,

Type 1: is partially upgraded. Where weapons / armor function as usual but have a [%] chance to cast skills or depending on the effect of the skill. Without changing the attack animation of the weapon.

Type 2: complete upgrade. Where the weapon / armor fully controls the skill. The skill is always active or depending on the effect of the skill. Changing the attack animation of the weapon.

I also see if this can be done, then you can get weapons with the skills you like.
For example: Shotguns + Rapid Fire = Assault Rifle Weapon (skill Type 2). No longer shooting like a shotgun but changing firing like rapid fire.

Of course there are several things that must be considered, such as the distribution of skill types for the type of weapon. Because not all skills can be used for all types of weapons and also some animations are not suitable for all weapons.

Maybe, to make it not too Over Power, it is better for each weapon & armor to be limited by having just 1 skill.