@arnottcr took a stab at this in https://golang.org/cl/247057, and the resulting change is pretty big and has ramifications like changing the names of user visible types. Unless we can find a simpler approach, I don't think we should actually do this.
While I find it problematic that one of the blocking arguments is that, type alias documentation is a bad ux and #44905 was closed without resolution; I agree this change is probably too large to justify otherwise, should we close it out?
I agree - we did not consider the references InternalTest -> T and InternalBenchmark -> B.
It does not make any sense to move testing.T and testing.B to another package and make them type aliases.
Let's close this.