Will they though?
Switch will sell boatloads, maybe even 10 million + on Switch alone (if it's native and not cloud), but last gen?
Most of the core customers, i.e. the ones with purchasing power of every new AAA game, have moved on to current gen, and even if you take supply chain / scalpers / demand issue into context, it's a minimal percentage OF THAT CUSTOMER BASE with purchasing power, who are left out. They'll be looking to buy a PS5/Series X than buy the last gen version.
Honestly, I'd be really surprised if the combined total units on PS4 and Xbone touches 5 million LTD.