The upcoming Ryzen 4000 would be a worthy upgrade, but it's very unlikely to have DDR5. The release of DDR5 will need a coordinated effort between CPU, motherboard and RAM manufacturers. That's why I think it's unlikely it'll be readily available until next year.
If it does become available this year, I'd still wait until next year. If DDR3 and DDR4 have taught us anything, new RAM launches are expensive and underwhelming. I wouldn't want to be an early adopter.