Question AMD Motherboard with DDR5?

Is there an AMD motherboard with a sWRX8 socket that supports DDR5?
No, that platform supports 8 channel DDR4 only.

I am guessing you are wondering if it would be possible to buy now and then upgrade to Zen 4 based Threadripper in the future?

There is no word* on if WRX80 based boards will get any future generational upgrades or not - my guess is no given Zen 4 is exclusively DDR5, however given that AMD uses a chiplet based architecture and the fact that the memory controller is on the IO die rather than the cpu die it's not impossible that they might be able to create a next gen chip for the platform.

Edit: *that I am aware of