I understand that the Mavic is wireless and supports 1080p output, but does the same output quality apply to the DJI 4?

Bump. Still need answer.

Don't see how it's possible. The HDMI module outputs 720p. Doesn't matter what the goggles - or any other device you use - is capable of, you're going to be seeing 720p. Not a definite answer - just my opinion.

At this time only the Mavic supports 1080p Output.  The P4 series is only 720p.