Though I agree that more bandwidth is (almost) always better, the 25Mbit provided by miniDV is ample to provide quality higher than what is offered by miniDV, even though "lossy" compression may have to be used to get there (don't forget that DV also is lossy). Temporal compression (i.e. between frames) is the way there.
As an example, normal SD Mpeg 2 DVD's have an average bandwidth in the order of 6-8Mbit/s, and that can already be progressive. So the step to HD (which should be okay with about 4x that bandwidth, considering equal bandwidth) should almost fit the bandwidth provided on a miniDV tape (25Mbit/s), and certainly should be okay on DVCPro50 media. Sure, it would be better to have all frames in and of themselves as complete images on the tape but if temporal compression means that I will get higher quality on the tape then I'm all for it.
I haven't seen the quality of JVC's HD material but technically their quality doesn't need to be inferior to standard DV footage, especially if it may be captured to full frames (and not IPB) during capture in real-time (can anyone confirm if the JVC allows this?).

Just my $0.02.

Kai.