Both seem unlikely:

1. Nintendo can and has denied rumours in the past.

2. The sources of this info came from some of the most reliable sources we have in terms of rumours. Eurogamer in particularly checked through their own sources and they're not in the habit of producing random click bait 

With any rumour its worth remembering that anything can change at any time

And yet the only thing that has change is the 400k a week switch was having all past months and weeks before all this BS, so...

Supply chain issues going on right now might be forcing Nintendo to delay announcement. I'm hoping the "pro" switch has enhanced mode for old switch games (frame rate) and prefer that new games not necessarily be exclusive (just have better frame rate and/or graphics in general). That way everyone wins. As someone who has held out for the "pro" at this point I understand patience is a requirement. The more frustrating part is going to be when pre-orders go up and in 3 minutes everything is sold out because of scalper robots. I hope Nintendo can somehow lock one or two consoles to an address to combat that...idk the logistics, but it would be nice to see effort in that direction.

You do realize it's just an upgraded Switch right? It's not a new system. Just as the Lite wasn't a new system. It's just a new model. They're not replacing the Switch, that is likely at least four years away. Nintendo always upgrades their portable systems, this is nothing new or strange, it's just normal operating procedure for Nintendo. You're talking about "Pro" which would refer to an upgrade, but describing it as though it is Switch 2. You're confusing yourself. Nobody is talking about a Switch 2, this is a new model of the Switch, just as Nintendo always does (see GB, GBA, DS, 3DS - they all did it). So to answer your question: the company has always done business this way.

I imagine framerate performance would be automatic right. Like framerate slows down if system can't handle it, more powerful system would keep those instances  steady. Now of course if you're talking about a game that's say locked at 30fps getting a bump to 60fps that would be something they'd have to go in and do an update. Same thing I suppose for resolution. Resolution drops will automatically fix itself in games where that happens, but to get an actual boost in resolution above what the game is set to do, or for example to 4k when docked, they have to go in an update the specific game.

My guess is they'll announce the new model at E3. It's not a new system so the idea of announcing it early so companies can announce games for it didn't make sense, because games for it are just normal Switch games.

Now it is possible that Nintendo will allow some third parties to port over exclusive "Premium/Pro/whatever" games from PS4/XB1 that wouldn't run on the other models. It'd be confusing for marketing games but I suppose it is a possibility and a way to market the new model as superior and get people to upgrade by having a little bit of an expanded library with games that couldn't otherwise run on Switch. If there are any games of that nature to be announced though I think it makes sense Nintendo would directly talk about them in their E3 show with the model's announcement, so again announcing the new model before E3 didn't make sense.

They said their direct will be entirely software related, so the only way they could announce new hardware at E3 is if they have a separate video/presentation in the works that none of us know about and isn't on the official schedule.

What if they announce it in treehouse?

they HAVE announced games in treehouse before (samus returns comes to mind)

they could also be bluffing.

There is precendent for that though. The DSi apparently had 5 games that only worked on the new model and not on the OG DS. And the New 3DS had 22 titles that didn't work on 3DS with Xenoblade Chronicles 3D and Fire Emblem Warriors being pretty notable ones.

Spec-wise these have been very minor improvements and the list of exclusive games are also very weak. It'll interesting if the Switch differs in both being a big power leap, which also then leads a to a major wave of exclusives due to the existence of PS4/Xbox One.

The closest comparison is probably Gameboy colour which truly had a life of its own and was still counted as a Gameboy total sales. 

IMO what will make this unprecedented is if Switch Pro is forward compatible with Switch 2 games but we won't find out for a very long time. The power jump will give us a hint though.