Okay after some more testing:
1) 1080/60p/50p files upto at least 40Mbits/sec bit-rates will play via DLNA, I found I had to remux to a transport stream to get them to play without stuttering, this isn't unique to 60p/50p videos either on the Panasonic. So we know these files are supported and they play back in glorious 60p as well, they are not downgraded.
2) An SD card from a Panasonic TM900 camera plays good as well when used in the Blu-ray SD card slot. I've been unsuccessful in creating my own content onto an SD card.
3) No amount of different tests has seen a single 1080/50p/60p video playing from a Blu-ray disc. Either copied as data or authored as AVCHD or Blu-ray. The audio plays but the picture is black. It seems the Panasonic is being very strict and ignoring the 1080/50p/60p video on Blu-ray media. It can play it back, the same video plays fine as per point 1 above, just Panasonic choose not to.
So my conclusion, if you want to edit 1080/50/60p files and produce a finished video, you can only play these back via DLNA, and lose the ability to skip back and forth.
I've not tried a USB stick or hard-drive, but these have caveats even if they do work as the Panasonic only reads FAT32 so you can't have a long video!
Certainly the hardware is up to the task, hopefully it will be more forgiving if Panasonic ever update their current players for AVCHD 2.0.
The above tests are using the latest firmware 1.70.