I've been peddling this idea since they ditched them. Their reason for leaving them behind was because they wanted more weapon choice rather than relying on a select few. The easy solution is to make all legendary weapons changeable when it comes to element. How? Etheric Light. Make it a consumable that when applied to a weapon gives it a random element. This way you may have to use a few to get the element you want on the gun you want. It'll have no effect in PVP and it will allow more customization in PVE plus it encourages PoE play. Simple.