“Further information about the successor to Nintendo Switch, including its compatibility with Nintendo Switch, will be announced at a later date.”
I think people are reading into the translated text what they fear instead of thinking through this logically. The rumored specs include joycons that don't mount the same as the old ones. Original joycons won't charge from the Switch 2 directly. You'll likely need an external charger stand or a charging grip for them. Switch controllers also may not be compatible with all Switch 2 software, we'll have to wait and see if they add buttons or new tech. The switch dock will likely not be compatible and possibly even switch chargers may not supply enough power. Additionally on controllers, Switch 2 controllers may be missing something like the IR camera or something else that creates some incompatibilities when using them to play original Switch games. They likely will not work at all with the ring fit adapter. There's more to compatibility than just cartridges and eshop and I'm sure if others really think about this and past Nintendo console transitions, you'll probably come up with a bunch of stuff I'm forgetting.
I can't imagine Nintendo has any intention of abandoning physical. I think there are still some countries without eshops and Nintendo is going to want to sell hardware and software there. So cartridges that hold full games is still important. They also understand the niche of phsyical game collecting and how well physical games have sold. I figure the cart slot will be slightly different to prevent people from sticking Switch 2 games into original Switch systems. My guess is a wider cart or a 3DS like tab. It's possible some regular Swtich games that are later in life of the Switch will start coming with, "Enhanced for Switch 2" labeling. So they can do some games, like Metroid Prime 4, as regular Switch games with that designation while not having to do a second sku for it. Of course this is Nintendo so they still could do something gimmicky with whatever extra stuff the new controllers do and do two skus again.