Just searching for 357 Max information over several years, I recall numerous people having tossed out the idea of a "rimless 357 Max" using 223/5.56 brass. At some point in the distant past, I have had on my bench both "357x223" and "44x30-06" dummy cartridges I cobbled together just for the sake of curiosity and conversation. My dad, not to be outdone, turned huge solid copper "bullets" to seat in brass 12 gauge shells for the same reason.
The idea of this "new" cartridge is definitely not really new, but it is interesting.
Useful, if it has similar ballistics to the 357 Maximum. With many states using the "straight-wall cartridge" criterion, it's a viable new cartridge.
I don't find it strictly necessary since I already have a 357 Max, which has a rim and my chosen arm tends to appreciate a rim (TC Contender).
It can be (theoretically) chambered in an AR. I've read that feeding was the snag for at least one person who actually tried this as a wildcat. Sorry, I don't even remember where I read it since I've been dismissive of the idea for a long time. Myself, I got a lifetime supply of AR fix in the Army and really have absolutely no desire at all to ever own one so I'll never have to worry about feeding problems, real or imagined.
Bolt-action? Sure, even though the 35 Remington is "better," it'd have to be a straight-wall for me to hunt deer with it, so if I insisted upon a bolt-action, I guess this would cover that base.
I'm happy to see a new straight-wall alternative, but I don't need it myself.
As a petty aside, I absolutely hate the name. Give something a name like that, and it doesn't live up to it, the flop factor is exponential. I'm just sick to death of stupid catchy names. and it may turn me away from a product I might otherwise benefit from, but it repulses me. Like I said, that part's petty. I like the 300 BLK but hate the name on that too.