IMO, outside of that platform it's utility diminishes pretty quick.
Yes, this. Kinda like a 5.7x28 in turnbolt.
In a turnbolt,
1. If you want a "full-powered" round or even a "mid-powered" round (i.e. not subsonic), then there are a million choices, from 7.62x39 to .223 rem, to younameit, with far more and far cheaper ammo choices - and more power to boot, even among "mid-range" powered rounds.
2. If, on the other hand, you want something dedicated to a suppressed round, although the .300 BLK is not a terrible choice by any means, in my view there are a few better ones. Since the bullet of necessity starts out between 1075 and 1150 fps, you need WEIGHT and DIAMETER to achieve better terminal effects on bad guys or game. That means .338 spectre or .500 phantom, if you must have the crazy high BC bullets. Or .357 mag, .357 max, or .38-55 if you want something with a big bore, easy to reload, and packs a wallop even at subsonic vels.
FWIW, I'm "working on" building my ultimate SBR'ed & suppressed hunter - it will be a T/C Encore (rifle) with 8 to 10" bbl (Bulberry, 1 in 12", threaded), chambered in .357 max and dedicated to the 230 gr "soup can" or "bowling pin" cast bullets:
https://www.pennbullets.com/38/38230tndrhd.html
Which of course, being a T/C, is not a turnbolt, but it would be a great setup/chambering in a turnbolt as well. The BC sucks, so it's not gonna be a 200 yard rifle in the wind, but out to 100-110 yards or so, it will be PBR, and with that weight and ultra-wide meplat, it will likely put a whompin on all but the largest game, even under 1000 fps.
Building a .500 Phantom would of course be THE ultimate suppressed buttstomper round, whether you put it into an AR10 or into a turnbolt or whatever. But it's very very expensive to shoot. My .357 max project is a poor-man's 2nd best alternative to a .500 Phantom or .338 Spectre - and talk about a reloader's dream.
Having said that, if one did do .300 BLK in turnbolt, it would still be cool and makes sense as a dedicated-subsonic (and suppressed of course), with the twist to match for up to 220s. But NOT as a supersonic rifle.
.500 Phantom and .338 Spectre info here:
http://www.teppojutsu.com/500_Phantom.htm
Can you imagine an AR10, select fire (or Slide-Fire), SBR'ed, suppressed, in .500 Phantom, shooting subsonic 750s? You could whomp bad guys through hard barriers to 300 yards with a little holdover, quietly, with not too much recoil. If I was a 1%er, I'd already have one!