IP with version number 5 is dedicated to the Internet Stream Protocol. Can you send such a packet on the internet at large, or will it be blocked/discarded?
No. A packet marked with v5 likely won't even be accepted by your WAN router. I don't think there are any somewhat current hardware devices with v5 support.
Some engineers just didn't give up but v5 was a dead end. It's much more practical to solve most problems on the transport layer and throw more bandwidth at it for the rest.