A2A doesn't do payment, and beyond those json cards it doesn't do identity either. It makes some of what DVMCP does redundant, but it doesn't make other aspects of nostr/cashu redundant. 

sambuca

Mmm its different stuff, doesn't work in the same way, also have centralization built in, ofc can be tweaked and just pick the best parts, but they are not the same

gzuuus_

nostr

DVMCP Updates, a brief why, what and when

Use A2A

https://developers.googleblog.com/en/a2a-a-new-era-of-agent-interoperability/