What will happen to all the parallel compute cards that will get upgraded soon? They can't be reused as GPU's for gamers, can they?

You're right; V100/A100/H100 "GPUs" do not have the hardware to display graphics and they generally require custom SXM motherboards. Most of them will sit on eBay for a while and then be scrapped when no one buys them.

If they can't display graphics they're not really GPU's at all. Maybe someone will think of a use for them. With an SXM-to-PCIe adapter board.