If there's a good and solid X to choose and use, I think the idea might eventually gain legs. As I've said previously, the primary warrior/arcanist in pop culture and fiction right now is the Witcher, with X being monsters and potions and defending commonfolk from said monsters. So if the game decided to incorporate the Witcher (or their own version of the Blood Hunter) into their class list, you might have something there.then the swordmage specifically fills the niche of 'is primed against dealing with X kind of threats' or 'uses X focus to defend against threats.'
The only issue is that I think too many people don't actually want that. They want the open-ended warrior/arcanist mechanics for the sake of mechanics so they can make their characters into whatever they want. But with the Eldritch Knight and the Fighter/Wizard multiclass already available to them and they just refusing them because those two don't have "special and unique" features and mechanics (which apparently seems to be the only reason to play a warrior/arcanist for those folks), they turn their nose up at them.