If you make faction items ALL faction only then you would have to make the items better for that faction and also make a heck of a lot of work to improve the weapons/items significantly or there would be a lot of empty factions.
For example - this idea came up years ago (when the Gaia Gauntlet was first introduced to NC) and someone said make it so that only Crahn Monks can use it. The reply was a resounding no. You would confer a massive advantage on that one faction to have Monks. Tanks would have a choice to go to PP, BT or possibly TT (for the cannon) and no other really good factions, tradeskillers would all lean towards FA and the spies would all end up as CA (if their armour was worth using). Rifle PE's would end up TS (provided again the weapons worked). No I don't like this.
The problem is you cant create some diversity by ADDING restrictions. That is simply not possible.
What would be good is faction specific weapons - within a specific class or classes but based on guns that ALREADY exist in NC but perhaps with a different colour laser beam or something else similar. We would want AT BEST aesthetic changes - IE many years ago someone else came up with the idea of adding some more stuff to factions like uniforms! You would have to complete your epic to get your uniform and then possibly trade a PA (just like the WOC system for armour currently) and you get given a PA for your uniform with the same stats but it gives you a different skin.
This i would like but not the restriction you came up Bruder.