Well...for me personally, not really. I wasn't overly fond of the gameplay mechanics - and the inability to turn the crappy gyro controls off - and if I want to play Johto again I'll pick up HeartGold or something. But I would like to see a Let's Go Johto because they're very accessible, particularly to younger players and those more interested in the mobile mechanics. That said, if there is going to be another game in this series, they NEED to fix the reliance on motion controls, because they're almost completely inaccessible to people with impaired motor skills, and that just isn't acceptable. It's not what Nintendo is all about, and not the kind of thing one of their core IPs should be putting out.
I am aware that you can use the control stick and buttons, but my god, those controls were awful and they were clearly tacked-on as a concession to the outcry that the initial announcement that these would be motion-controlled only just because received. If there is to be another game in the series, it needs the option to choose between proper traditional controls, motion controls, or a blend of the two. Current year argument, but for fuck's sake, it's 2020, including options for how to play a game isn't bloody rocket science. This is the thing with Nintendo games in general - they're always striving to offer new experiences, but the problem is that they force them onto you by removing all other options. For a series like Pokemon, which is obscenely popular and has a reputation for being something anyone can just pick up and play, excluding people this way really isn't acceptable. Not when you consider the ONLY reason it was so heavily motion-based was "to provide a new experience" and that was it.
So yes. Another game exactly the same as Pikachu/Eevee only set in Johto would not be good. One that learns from the mistakes of its predecessor and adopts QoL changes in how it is controlled at the very least would be great. That's not an unreasonable ask, either.
The mascots should be Pichu and Pikabl--I mean, Marill. Yeah. Marill.
But I also have a very strong feeling that a Let's Go Johto would not include Kanto postgame, because they're very low effort, low budget titles in how they look and feel. Which ironically is more polished and thought-out than SnS, but they're clearly designed to be stripped-down, simplistic versions of the games that incorporate mobile mechanics. Such a game does not lend itself to having a massive postgame.