I guess WBY has seen the writing on the wall and decided to step up it's game. WBY brought velocity and the concept of "high quality" to the game decades ago, but I'm sure they have seen their market share plummet in recent years. WBY had always appealed to the high end market, but these days people that want good stuff have way more options and want precision.
"Double radius shoulders" and "freebore" are so old school that few will still fall for that nonsense anymore.
WBY has painted themselves into a trap. WBY style cartridges are not in favor anymore, and for good reason. I doubt this cartridge will catch fire. It ain't no 300WSM or 375 Ruger
I expect with the Vanguard line of good quality - working man priced rifles, the availability of non Weatherby chamberings in Weatherby rifles, and the availability of affordable brass for some Weatherby cartridges from other manufacturers, Weatherby's market share is greater than its ever been. While its true that there is a great selection of high end rifles available to the consumer, there are those who are doggedly brand loyal to Weatherby. While propriety cartridges will never be as popular as standard cartridges, I don't see the Weatherby's line of cartridges disappearing any time soon. Weatherby has been around since the '40s, but what has become of Lazzaroni? So I'm not sure what trap you might be referring to, other than Weatherby carving out their own niche in a tough and competitive market place.
As for the comparison of Weatherby cartridges to the .300 WSM or the .375 Ruger; the .375 Ruger makes sense to me, when its chambered in the Alaskan rifle. The .375 Ruger provides adequate power, from a compact rifle, while producing modest recoil, and its at its best when loaded with light to mid weight bullets. There is nothing in the market place that is better in the role of a dangerous bear rifle, for use in thick cover. But the .378 Weatherby is more versatile, is better suited to African and Asiatic dangerous game, and outperforms the Ruger by a significant margin, to the extent that it will do anything the .375 Ruger will do, even when throttled back to 85% of it's potential.
Personally, I see little point in the .300 WSM in the context of .300 magnum rifles. That is not to say its not a good cartridge; IMHO, it fills a valuable niche, but it should not be viewed in the same light as a .300 magnum. The man who wants .300 magnum performance is better served with a long cartridge like the .308 Norma, .300 Winchester or the .300 Weatherby. Long bullets like mono-metals or Berger's popular Hunting VLDs, must be seated out so far in the .300 WSM, so as not to interfere with the short powder column, that it would have to be used in a long action rifle, and if it's velocity potential is realized, the barrel needs to be as long as the full sized .300 magnum's. Even when the .300 WSM's velocity potential is realized, it lags signicantly behind the .300 Weatherby. If the .300 WSM is chambered in a compact hunting rifle, which was the point of it's design, its comes closer to .30/06 performance . . . which isn't bad, but its no .300 magnum. Therefore the .300 WSM's niche is better directed to the hunter who might be considering a .300 Savage or .308 Winchester but wants just a bit more, from his compact rifle, either for hunting larger species of game, or just for a flatter trajectory. Viewed in this light, the .300 WSM is an intelligent choice, but I believe it would be a mistake for the rifleman who wants .300 magnum performance to choose it.
Will the 6.5-300 Weatherby be a commercial success? The interest in high velocity small bore cartridges is certainly there, and the American market place appears to have finally opened it's heart to the advantages of the 6.5 bore. The 6.5-300 Weatherby wildcat has been with us since the late '60s, so I have no doubt that it's legitimized form will be with us for some time to come.