While I don't really have an opinion on an experience which neither I nor anyone here has had yet, and while I also think Celtic Fyre is a not-particularly-useful proxy for whatever this thing will be -- just for fun, let's turn the offered logic around and see how it goes.
Would you pay $50 for a Celtic Fyre showcase, even if it were only 2 or 3 or 4 performers, if the show were done semi-exclusively just for you in a group of 25 people or fewer, in some sort of extended format that lasted longer than 25 minutes end to end (even if it was just a few 10-minute spots over the course of an hour), with you and at least one friend/loved one sitting at a reserved table just a few feet from the talent, not a bad seat in the house, in a cozy old-timey bar themed venue just for the two dozen or so of you, with probably some interaction with the performers, and with your choice of a 3-drink flight served to you?
I think a number of people would pay for that experience. Enough to make the expense of creating the experiment worth it to the park. In fact I think that would command more than a $50 rack rate (though again, I think the CF comparison is a bad one, as I doubt any entertainment in the room will involve Fyre-heeled waiters).
I kind of suspect the "one-of-a-kind immersive bar experience" will just be exactly that: a nice semi-exclusive bar setting, plus two charismatic servers to mildly humor and entertain while you take a break for an hour or so in your own little speakeasy. I base this expectation on nothing concrete except the price point, which for a theme park doesn't seem exorbitant. Considering what people seem willing to pay for other small-group park experiences, $40-50 is not a particularly huge hill to climb. Just like dining with Elmo or petting horses: honestly, for most people the experience is fine. It's the perception of exclusivity that, for many, really justifies the additional price at a big theme park for a decent bolt-on experience.
(...For a decent bolt-on experience...)
Can the park deliver on something like that? Different question. Maybe it works, maybe it flops. I think the demand probably is there, though, to either be engaged or run off.