1. -c no longer implies --no-psqlrc. That's a backwards incompatibility, but very easy to explain and very easy to work around.
This can be very surprising change. Can we disable it temporary by some environment variable? like NOPSQLRC ?
2. You can have multiple -c and/or -f. Each -c is processed in the traditional way, ie, either it's a single backslash command or it's sent in a single PQexec. That doesn't seem to me to have much impact on the behavior of adjacent -c or -f.
3. If you combine -1 with -c and/or -f, you get one BEGIN inserted at the beginning and one COMMIT at the end. Nothing else changes.
As long as you put only one SQL command per -c, I don't think that this definition has any real surprises. And we can discourage people from putting more than one, saying that that will invoke legacy behaviors you probably don't want.