I imagine you'd be able to get enough people interested in it. The trick is finding a good gear class for it and distinguishing it aesthetically and gameplay-wise from existing jobs (especially, DRK, NIN, SAM and RDM).
Best guess, though, its being a Mystic Knight could only carry it so far, and you'd likely have to instead incorporate those aspects into a related original job.
Take, for instance, a Scouting-class with dual scimitars (too many swords already, I know), a Staff, or a Bladestaff (perhaps with a blade on each side).
Actually, let's go with the last by way of example, and use it as the excuse for differentiating stabs (front blade), slices (back blade), and whirls (both strike), since that'd in turn give reason for a fun unique mechanic like enchanting the front and back blades separately.
Okay, so we have our silhouette and a core gimmick. But we'd still need to synergetic aesthetics, a place of origin, etc.
Let's say the job came from... Thavnair, as they've got quick elemental imbuements aplenty, along with good use of magical/artifact weapons, related seals and scripts, and would likely have reason enough to develop a martial art around that.
Okay, now, how does the Thavnairian aesthetic intersect with Scouting? More than likely light, probably open-chested tunics, loose pants, and/or wraps, etc. It's simultaneously direct but slightly ornate, slightly showy. And if we're to have a Mystic Knight but not make it a Maiming or Fending class, there'd have to be something foreclosing that possibility.
For instance, lets say that a second aspect of this Scouting "MSK" is that it's a master of distraction, opposite NIN's mastery of stealth, able to offer defensive support opposite NIN's offensive support. It has quick attacks, alternatingly flurries of stabs or whirls of sweeping strikes, has Ice, Fire, and Wind magic, with Lightning and Water being possible by combination (melting Ice for water, and creating imbalances between enemies' heat and then adding wind to create lightning)... Perhaps it's even able to leave an ice-dummy or an ally to lock a targeted mechanic to a particular baited position or to provide allies with a burst of speed via wind magic. Atop this, maybe it has specific wards that it can use to either suppress incoming magic damage or to allow for a deeper combo on an enemy (preventing elements from dissipating or combining for a time, allowing them to stack higher).
...From all that, maybe something like a... Dervish?
That's just one spitball way of routing to something likely able to be sufficiently fleshed out while playing on and amping up oldMSK (MYS?)Mystic Knight aspects. But hopefully the example seemed sufficiently fun.
I wasn't advocating for that, or any other, acronym for Mystic Knight or Spellblade; it was just a quick shorthand to as not to use the full name in the last line and therefore make clear that that was NOT the name I was proposing for the final product, for those who'd skip most of the post.