So, I don't know if this is possible, but let's suppose you have some footage that would best be archived to HDV tape, but you've already cleared it off the card. Can you copy it BACK to a blank card and then play it out for the downconvert?

You could just hook up your HDV device to your computer and play it out without going out to the card again.
Save you a step.

Currently I'm using Avid Liquid (although beginning the switch to FCP) and playing it back out without rendering isn't an option... I don't think. And the way I have to import into Liquid costs me the timecode. PLaying out from the camera to a HDV deck lets me keep the timecode and no rendering.

I did have a chance to try this today, and copying the files back to the card seems to work fine.

I had archived some footage to DVD-ROM, to save the originals from the card, and I wanted to re-load it to the camera to show it to someone (camera was easier to carry than the computer. I just copied the files back to the card via the USB and it worked just fine.

I'd like to export an edited FCP sequence back to the card to be able to use HD-SDI out to a deck (don't have HD-SDI card). Can this be done?

I'm curious about this too. In the past, Sony cameras have had some "undocumented" features regarding playback so it may be worth playing around with this.

In my case I want to hook up the camera to an HDTV to show an edited sequence to a client.

The alternative is to go the Apple TV route but it's only a max of 720p24 or go Blu-ray, which I will do eventually.

In the meantime I wonder if people have tried various experiments back to card for playback from camera.

I'd like to export an edited FCP sequence back to the card to be able to use HD-SDI out to a deck (don't have HD-SDI card). Can this be done?

You would have to find some way to rewrap the MXF file back into an mpeg4 wrapper and keep the folder structure in the BPAV folder intact to fool the camera into thinking it was an original clip.

...something to play with