Supporting v1 API over gRPC would make it easier for people to adapt the v1 API, and Mesos in general:
1. The current HTTP API is not easy to use.
2. gRPC is a popular RPC framework.
3. gRPC can support different language bindings.
Since v1 API is based on proto2, the plan is to declare gRPC services in proto3 but uses the existing proto2 messages.