Personally, I think one major problem with porting the old Pokemon games to the Switch would be the long term if they put it on Nintendo Switch Online like they do with their old games, since if the service shuts down (like what happened with WFC), then...What happens to the Pokemon? Obviously, they'll very likely put in compatibility between those rereleases and Pokemon HOME while it's online, but if the game is offline, that's probably out the window.
Hell, forget the Pokemon being unable to be transferred, what happens to the game itself if the service is down? If you have an original gen 1 or 2 cartridge that's still working, you're not able to transfer them to gen 3 but you could still play it, whereas an online service going down with a game playable only online? Yeah, no. The save file will still exist, but it won't be accessible to actually play without some weird emulation or unofficial servers made by fans. Massive headache for the future.
If they were to rerelease the old games, I'd hope it was individually to purchase and own forever, without needing online to play it.