I think at this point it's basically a non-option though. Ti is nowhere near mature enough, the ops investment cost is extremely nontrivial, and it and still has some interesting issues to work out (e.g. [1]).
Furthermore, protocol-compatible doesn't directly imply API-compatible (I'm thinking of very very subtle differences between things like datatypes or isolation level behavior). I know a bit more about CockroachDB, which consciously does some things differently from Postgres.
TiDB developer here.
There are more than one hundred companies who use TiDB in their production environment. The number keeps growing. The link in sanxiyn's post shows part of them. I think it is safe to say that TiDB is mature enough.