6 is mainly to solve the caps matching failure in the place where it belongs.
No transform care about mismatched fps as of today and there is no reason we need to call gstreamer for something that would pass through buffers but change fps, this can be done on the client side.
There's plenty of cases where clients can set mismatched fps in their media types, and as far as the tests go this is never a reason for a failure.
Regarding 7, it is going to be needed to fix some frame size / padding issues when clients set it on input but miss it on output, or set a new output type with a missing aperture but overall matching frame size. The decoders we have currently workaround this by clearing the frame size before set_output_format, and this is incorrect.