Sounds like the 375 Epstein wildcat without the belt (the Epstein is a 338 Win mag with a short neck opened to 375).

What could be interesting is Hornady's loads for this. If they use their proprietary powders in their Light Magnum or Heavy Magnum, they might get factory 375 H&H velocities.

However, I don't see any improvement over anything we already have. I don't see the magnum length action as a hinderance, at least not to me. If someone would build one svelt enough, like the pre-64 Winchester (opened up standard length action). Right now, most 375's on the market are too heavy for the chambering, in my opinion. The RSM is heavy and the CZ much too blocky. A bare rifle in the 7.5-8 lb range is plenty enough for a 375, especially if you are going to scope it. That would bring the rifle to 9 lbs+ which is on the max weight side of the 375 to me.