I've been closely watch the NSO "leaks" for quite some time now, and while I'm personally holding out hope for a Crystal-esque appearance of the Gen 3 games (more specifically, having stuff like how that Celebi event was), I'd like to reiterate for anyone wondering that nothing's actually been confirmed yet... or has it?
Here's the funny thing about the Game Boy saga when it comes to Virtual Console. The GB and GBC were playable on the 3DS, and (I don't count that stupid ambassador thing from 2011) the GBA games were almost entirely placed on the Wii U instead. Why do something like that, you may ask? For the purpose of the Pokémon franchise, the GBA being properly on the 3DS wouldn't have been as special as, say, the Gen 1/2 games, since we still had ORAS at the time for Hoenn fans to try and enjoy. For the large majority of other games, I believe the reason to have something to do with the Wii U GamePad. Back before I started playing games during the seventh hardware generation, the sixth generation allowed the fewer consoles that were out at the time to be more inter-connective than today's systems, a sign of the changing times if you ask me. Any 6th Generation Nintendo fan should know about the Game Boy saga's connectivity with the GameCube console by now, and I think what Nintendo's "no 3DS, only Wii U" decision was aiming for was to more accurately represent Game Boy era emulation than anything that the original Wii console wasn't capable of. (Imagine playing Gen 3 with a sideways Wii Remote, yeah no.)
That doesn't state why things are confirmed, but it actually kind of does, and here's why. If we take a look at the list of games made available on the 3DS and Wii U's end for every part of the Game Boy saga, we'll see that the games were separated onto one system or the other depending on which it plays better on. Furthermore, the handheld Switch (and the Switch Lite by extension) is notoriously similar to the Wii U GamePad, at least as far as playing on the tablet itself is concerned. This matters because the Virtual Console lineup is actually a lot more similar to what these leaks are suggesting than meets the eye. In fact, the Switch's hybrid nature relative to the Wii U would explain why NSO could try and emulate games that, say, the 3DS could and the Wii U couldn't or vice versa. And what better sub-group to work on that hybrid transition than the same guys who've already successfully ported NES, SNES, and N64 games presumably based off the other 8th Generation hardware? Heck, they even got the GameCube to work if Mario 3D All Stars counts for anything.
TLDR; people tend to forget that the Nintendo Switch is still very much an 8th Generation system, and this is why the bulk of NSO support should only be coming after the 3DS/Wii U eShop closure anyway.