isnt pokemon already open world? (bar occasional snorlax blocking)

Not really. There are some branching paths here and there with items to find but the game's map is mostly linear (As far as I remember at least, last one I've played was Y on the 3DS). In any case, when I say open world I'm basically referring to those games with giant maps and a ton of empty space between the actual game content. People may like it to "take in the scenery" or whatever, but to me it's just plain tedious.

"Rebooted" could mean a lot of things. Could mean something like core mechanics and franchise tropes are getting re-hauled ala BOTW or it could mean they're literally starting over and pretending nothing else before it exists. Or it could mean some kind of reboot using remakes of Gen 1.

Assuming the Switch game takes advantage of the hardware, I'd be surprised if they didn't; properly animating the better part of a thousand creatures for the first time would be a nightmare.

I know several people (most of them female gamers) who only play Pokemon, Animal Crossing, Kirby and a few other of those "easy-going" series. Pokemon's turn-based nature is the only reason why they like the gameplay, so going too much in the action direction could alienate a lot of people.

What do you mean that would be boring?! Everyone loves Gen 1.

- GameFreak's thought process. 

Smash does the same, but you don’t hear people babbling about changing the battle system.

It’s like everyone holds a grudge against turn-based combat (especially so-called critics) while it offers the most depth and requires actual thinking.

There is 800~ Pokemon at last count.
A reboot/remake/remaster and a return of just the classic Red/Blue I would be super keen on.

I would even buy a Switch just for it despite the unappealing hardware.

Plus it's probably a tall order making essentially 800~ "next gen" Pokemon models for the Switch anyway.

Wasn't there a post near SuMo that said the models in the game were HD and assets were ready , but they dumbed it down for the 3ds?

Well you can't blame them, if you ask any general audience, they'll probably only recognise gen 1.