Inbound GRPC will be limited to HTTP1.1; that's a limitation of the platform rather than the language runtime. We're working on HTTP2 support, but I can't promise any timelines.
By inbound GRPC you mean when running an app engine instance as a client right? So running a GRPC server is completely out of question still I would presume?
I mean running a GRPC server, yeah. It's a limitation of our networking stack which we're working on fixing.