I always assumed a Pro model would be new hardware especially after the Nvidia leaks which had stuff that a normal switch would not be able to do. Like the Super Nintendo was not a souped up NES, it was all new hardware and the word Super was just a branding thing, I figured the word Pro would be used in the same way.
The system may have a whole new name entirely, without an official announcement people just use assumed or agreed upon temporary names. And the switch has been out for around 6 or so years, that's usually time when new hardware gets announced. Sales have slowed down for it which means it's reached it's saturation point, what happened with the PS3/360/Wii generation was that hardware sales slowed across the board so much (this was because all 3 systems were out for so long that they all reached saturation) that people thought consoles were on their way out and manufacturers did not want that to have that kind of appearance again.