If the switch was "Thicker"(lol) it could have a bluray drive on the back .
something like this:
If random people could do this, I expect Sony to do it in a masterful way, without those big bezels obviously. There is no need to "switch" to carts, A Bluray drive can fit just fine . Also because we all want the PS5 to be BC, if they put carts if would not be possible.
Is this possible? Sure. Would I want to buy this? Hell no. I wasn't really even a fan of the PSP disks, and those were a lot smaller than a Blueray disk.
Part of portability is having small and durable games, so that you can easily take several with you on the go.