Another mistake that gamers make is to think that having more options is always better.Ill quote Delio because he basically encaptures what I think about this subject:

"An improved Switch is the most reasonable option.

Price wise, if the improved version is more expensive, then, by comparison, the Switch OG model would look cheaper. And with time, with lowering price you'd eventually reach another audience without the need to compromise your future.
An improved version would, in theory, allow for more multiplats and ports to arrive to the system.

A mini version that makes it a handheld is the same as rejecting what make the Switch a success, it would also make it seem like an inferior product. Why should people opt for a mini version when they can't get the best experience on the original Switch? The potential of a such a model would be limited by default.
Not to mention how certain games would be affected by the fact you wouldn't be able to detach the controllers.

One of the main reasons that made Wii U fail was poor comunication.
Having the communicate that you have two devices that do not work the same would sound messy and awkward. Not the best thing when you want to market multiple products."

One thing that I would add is that it makes more sense to launch a Switch Pro(that just bumps things like battery life, screen resolution and so on) after the base Switch has already been discounted, so you would have 200 or 250 dollars version and a 300 or 350 dollars version.And for that, the base version still needs to be discounted.So thats why I dont think this revision is comming in 2019, even if I do believe it will happen(A Pro version, not a mini one)

For your question of how many games need the joycons, out of the top of my head I know that 1-2 Switch, Super Mario Party requires joy cons.Pretty sure there are more games.But not only that, but there are also games that have exclusive features that revolves around the functionalities of the Joycons, such as Mario Tennis with its motion controls, Senran Kagura(For whoever likes those games lol) and probably many more in the future.Not to mention that you lose alot of value not having them detachable, since you basically come with a second controller out of the box that you dont have to pay extra to have.

More options is better. Sony is better off with PS4 + PS4 Pro. Microsoft is way better off with XB1 + XB1X, infact sales of both of these systems would be showing late gen fatigue by this point without those new models, instead they are performing very well. Apple is way better of with multiple iPhone models.

The whole "one model for everyone" is a tired and outdated 1980s concept. 

I think it's more likely to be a Pro version (I actually would prefer the name Super Switch, reminiscent of Super Nintendo). Go watch SuperMetalDave64's and RevieTechUSA's Youtube Channels. They both have leak sources confirming the Pro version.

Wasnt SuperMetalDave the guy who swore up and down that Nintendo was going with AMD instead of Nvidia and it would be more powerful than PS4? Ya I dont trust his leaks.

I could see them doing it with or without detachable Joycons.

It is just a matter of what choices they make.

Joycon only games use separate Joycon either way, its just a matter of if they are stowed and charged by the handheld unit or not.

I think the clam shell design makes the most sense for portability and compatibility, but the joycon-less design would obviously be the cheapest manufacturing wise.

Maybe they have more imaginative engineering, who knows, but I think the goal whichever way they go is to have this new model ready for next year to launch at $199 along side Pokemon 2019 or Animal Crossing.

The sky's the limit of what kind of revision it could be. It could merely add more storage and a few other tweaks. Or it could upgrade the hardware a significant amount. Awaiting details from Nintendo.

But AMD was just his bold prediction it was not based on a leak he had. Seriously, watch his video regarding Cyberpunk 2077 where CD Project Red makes clear indications regarding a Nintendo Switch version. They said something like the current version of the Nintendo Switch couldn't handle it which is in context a clear indication that a more powerful Nintendo Switch is in the works. Otherwise, they would just have said that there will be no Switch version or that the Switch is not powerful enough, period.

The discussion between SuperMetalDave64 and ReviewTechUSA regarding the topic is also worthwhile to watch.

And seriously, please don't think anymore of Nintendo as this awkward, egocentric and stubborn company that don't give a damn about what actually 3rd parties want. Nintendo has changed. They still go their very own way (which is a good thing) but they have learned to listen to the market. Nintendo knows very well that the current Nintendo Switch can't handle/poorly handles triple A 3rd party games. They also know very well that Play Station 5 and Xbox Two are around the corner and that once they are on the market, 3rd party triple A games will be impossible to port to the Nintendo Switch. And finally, Nintendo knows very well that they need 3rd party triple A games to stay competitive. Therefore, it's only logical that they come out with a Switch Pro. No, technically it will not and can't be at the level of PS5 or XTwo but it will be at a level where 3rd party triple A games can be ported. Years have passed since the Tegra X1 came on the market, portable technology has made a huge step forward in the meantime.

That sounds a lot like speculation.

We all just speculate here - or is someone an insider?

However, we enthusiasts searching for bits and pieces on the internet, youtube an co. to make an educated guess of what's coming. Every researcher for every topic will always try to find evidence for his thesis, of what he believes or of what he would like to be the truth. There's simply no real independent neutral researcher. Everything is kinda fake. That's why we have discussions here and it's a good thing.

But please explain me then why such a thing like Resident Evil 7 - Cloud Version and Assassin's Creed Odyssey - Cloud Version exist? The make absolutely no sense. I believe that behind the doors there are talks between Nintendo and 3rd parties on how certain triple A games could be ported to the Nintendo Switch which in turn plays into a possible Switch Pro.

Speculation is fine but a couple posts back you said it was leaked sources.