Well, objectively speaking I don't need anything. But I wouldn't mind a custom flash hider which is basically a solid cylinder with three smaller cylinders bored into it. The solid cylinder fits inside the RIS(not further than 2 cm behind the threads), the first bore is wide enough for the outer barrel, the 2nd is threaded (or contains metal threads glued in) and the third is to take the BB.
Effectively making the gun end 5mm after the inter barrel, which itself ends 1mm after the threaded outer barrel, which sits 1cm past the RIS. Tapering the end pointing towards the receiver would be nice too.
This is a description, not a design.