Well, Tripwire itself said that the very purpose of these guns was to AVOID making anymore crossperk weapons. The main reasoning behind that was that it was often difficult to design a gun that was effective in the hands of two different perks (and one can see why : very rarely does a weapon gets used by two perks in the same way... Does anyone ever uses the HX-25 or Spitfire in the hands of a gunslinger?)
Not that I wouldn't mind to get some of them in the hands of others (the buckshot for the 'slinger sounds like a great idea!) , but most of them would just be redundant or just barely practical.
The Incision is pretty much the medic's Railgun. It wouldn't bring anything new functionally, even if its stats are a bit different. Similarly, the Teslauncher is pretty much the Helios Rifle.
Meanwhile, the kaboomstick wouldn't work in the hands of the support because he's so reliant on extra penetration. If the pellets simply EXPLODE, it wouldn't put forward the support's pros. And if they don't explode... Then you'd be better off using the boomstick to begin with.
I could see the Incendiary Rifle for the Commando (I mean, the SWAT does have the MAC-10 right? Plus, the M16 used to be a commando weapon as well in KF1!), but for the demo...? I see no real reason. The regular M16 with its grenade launcher is pretty much Demo's version of the Incendiary Rifle.