Author here: Sorry that I was so harsh on textproto. You are right that it has some strengths over JSON... I'm actually a fan of JSONC for this reason. It does limit you on tooling... but so does textproto, right?

I think the bigger thing that I'm worried about is that gRPC has so many mandatory features that it can become hard to make a good implementation in new languages. To be honest there are some languages where the gRPC implementation is just not great and I blame the feature bloat... and I think textproto was a good demonstration of that feature bloat to me.