I don't know of any that need some final push. I would think it would be better to just contribute to kde or gnome ui/ux wise. I would say my distro but I almost never click the scroll wheel and just tried it out and it does paste on middle click. No idea why that would be a deal breaker. Also have no idea what windows does on middle click even though its been the majority of what I used day to up until a year or so ago or for the mac even though I used it in the late aughts.