The advantage of a slightly upgraded SwitchTV would be yeah that people who don't want the portable aspect at all might be convinced to get a Switch at a cheaper price, if say let's say a SwitchTV would be like $220 and comes with a pro controller. Plus if its slightly upgraded they could play with a little higher res or framerate or whatever to get that premium Switch experience, like say its strong enough to play pretty much any Switch game in 1080p/60fps.
A much more powered SwitchTV is an option, but it'd just be a 4k Switch, so the question is how many people really care about buying a more expensive Switch just to play with really high resolution? It wouldn't magically make games have Xb1/PS4 level graphics, it'd just play games in 4k. I would imagine there are more people out there who would only play at home and would pick up a cheaper home-only version of a Switch than there are people who don't have a Switch just because it isn't 4k and would pick it up if there was a 4k version with no other graphical upgrades.
I think a theoretical SwitchTV would go with the cheaper route, trying to pick up people who aren't interesting in portable play but would get a Switch if it was cheaper. That could potentially be a few million people. And now that Nintendo has abandoned the "purely Switch" concept with the Lite, I think you could view the Switch concept now as just being "you can play however you want to play" which means you can buy any kind of system you want: portable, hybrid, or home, with portable being the cheapest, hybrid being the most versatile, and home being the premium visual experience at least by a little while still being cheap. I actually think this might be more likely than a premium hybrid Switch right now, considering that Nintendo still hasn't cut the price of the Switch, I think a premium Switch hybrid would be more likely after a price cut so that the new one could be at $300 and they'd probably eventually phase out the original Switch.