I'm on Windows and I have the same issue. I specified the interface with the % notation (it clearly does something, because if I put a wrong interface number, it gives me "general failure" instead of a timeout). The flag -i is for TTL, not interface.

However, if I do the same from my rpi, a few devices respond (my tv box, the rpi itself, etc)... including my windows machine!

According to https://superuser.com/a/467559, "The Windows ping program cannot send a ping request to broadcast addresses". That's multicast, there's no broadcast in ipv6; but maybe there's the same issue. I tried a quick https://learn.microsoft.com/en-us/dotnet/api/system.net.netw... and it times out too.