Largest Switch cart currently available is actually 64gb. Tho since few Switch games exceed 16gb, 16gb is the largest size used in general. Most games that are over 16gb just use a 16gb cart and include a code to download the rest. Only a couple dozen using the 32gb variant (eg Witcher 3). Dont know if any games actually use a 64gb cart. Maybe NBA 2K23 or NBA 2K24, but given those are both 2K cheaping out by just being roster updates of like NBA 2K20, I doubt they shelled out for the largestt size.I don't really think the physical console needs to change all that much. And certainly the carts have enough space to support pretty much anything. The Switch 2 only really needs to change the internals to boost it's power.
That said, Switch carts aren't actually traditional rom carts, but basically flash memory in a proprietary form factor. There's no technical reason preventing Nintendo from offering, say, 256gb carts, but I doubt they will cuz of cost.