Wow, I edited in the same idea before I read your post there. Great minds must think alike. We can only assume that stuff is a recent development in Star Wars universe.
Or suppressed. We know that the tech exists (
edit: ninjaed) but how widespread?
Jedi council wouldn't (even in its beneficence) be too keen to have anything that's sabre-proof, just like they don't encourage non-Jedi to take up their own traditional weapon.
The Sith Lord of a (theoretically) Jedi-less Empire wouldn't be, either. It's their domain and their prerogative, after Order 88/whatever.
But the First Order knows that there's still
some experienced Force opponents on the books, even if they're not that active, so as long as they can restrict the plasma-riot-baton thingummy to their own forces (mostly justified in it being also useful against non-Jedi) it might be a useful countermeasure for their elite mooks. (Ok, so they were probably expecting Luke or Leia to be the ones, not a random guy with no background in the art or a heretofore missing Force-savant whose metal wasn't even tested against the Riot Control trooper...)
And I'll have to see if I can find out the tech behind some of the Podracer 'power linkages'... Possibly it (sabre-like) holds some separately floating modules together (if it isn't just a separate tractor/repulsor-based tech), seems to transfer power, and yet can go through the ears of a Gungun (albeit one protected by inbuilt latent force-use, or just comic-relief styled plot-armour) without killing it by any number of ghastly ways.
With the sabre being traditionally tunable by the Jedi who wields it (blade capable of cutting through blast-shield, or a safely hand-holdable solid so that it can even be used as a viable crutch), either by the sheer Force of mind or some dial on the hilt right next to the one that adjusts its length, I imagine that Kylo's crossguards
could be non-self-cutting (as required). (Ditto the power-linkages, if not
intended to be flesh-searing... Or safety-dampeners connected to sensors that detect accidental interuptions.)
The big problem with equating a lightsabre with a big dumb (albeit shaped and possibly sharpened) lump of iron is that a lot of swordfighting techniques (outside of show-fighting, where you need to be careful) rely upon the sheer mass of the sword. Unexpectedly being hit by the weighted pommel and cross-guards/knuckle-protectors is a valid move if the one doing so doesn't let their
own guard down. The finely-tuned physical device that is the hilt doesn't have that much of a heft to it (at best, it's like using a torch... and not one of those honking big Maglite ones that security guards and the like tend to go for, weighed down by the whole string of D-sized cells inside its ruggedised casing) and we're never really told anything about the 'weight' of the plasma blades. We're left to assume that they probably contribute less inertia than styrofoam would, the damage being the 'burn' and the strength (both physical and mental) of the wielder as he/she forces it (again, perhaps both physically
and mentally) against the opponent's similarly adamantium-like blade.