"There is nothing new under the sun." That is the .357/44 Bain & Davis and it has been around since the '60s. As to your question about pressure, a qualified engineer could give you more info than I can, but I believe the factors that determine the pressure any cartridge operates at are not so much determined by its shape as how it is loaded. Even fairly radical shapes have been successfully loaded and used safely.

Years ago, someone developed a .22-.378 Weatherby cartridge with the idea of producing 6000 FPS in a conventional rifle. The project wasn't undertaken as a serious effort to produce a marketable product. It was just an experiment. I don't recall anyone getting hurt.

The conversions you are talking about a pretty tame compared to something like that. Bottom line with this stuff is, "How useful is it?" The .38 AMU was way more productive than the .38/.45 Clerke ever was, from what I can recall.