I expect this is really just a veiled attempt to garner evidence for a case against the .350 Legend.
The .357 maximum had multiple marketing and technology issues in it’s flagship platform, the limousine Blackhawk, which were largely enough to sink the cartridge into obscurity.
In Encore/Contender single shot rifles, the .357max is a hoot. Very inexpensive range ammo for the reloader, yet with substantial capabilities at short ranges out to 300yrds, and exceptionally efficient on game up to and including hogs and whitetails. As I often state here, the .357mag is excessively restricted for range when used on game, which the Max tends to overcome. A 44mag, it’s not, but significantly more than a 357mag, it is.
As a “tweener,” it doesn’t fit into a Marlin 1894 length action, but isn’t long enough to make good use from a 336/1895 action either. Some actions do exist which can contain the pressure and swallow the cartridge length, but these are relatively low volume. The demand for leverguns is low in the market as a whole, and the demand for a boutique cartridge in one, which requires its own specialty design, just isn’t there.
In a magazine repeater, the rim is a challenge, and again, the interest largely isn’t there. The Ruger 77/357 & 77/44 fell off of the map for a reason, folks aren’t buying them in sufficient volume to support the production line. The .357max would be yet more obscure in that already obscure niche.
But there are plenty of guys out there who have been replicating the performance of the 357max for years, especially in AR’s, and considering over 10% of American States restrict rifle hunting to straightwall cartridges, having a magazine friendly analogy to the 357max makes a lot of sense in 2019.