Just to conclude the discussion from my end.
I gave the raspberry pi a few more goes and then gave up.
I have got a nice z83 TV box running windows 10 that can run off 12v/1.5A so could be battery powered working.
The footprint isn't too much bigger than a Pi and it has 32GB storage and 2GB RAM which seems to be OK. I use a similar box for my WiresX node. For the project that M0BPQ and I have been discussing i.e. an HF Rx igate it seems to be ideal. RAM and Processor (4 core Atom z8350) definitely ok for this. More powerful systems exist in the TV box market, I have one running my WXSat decodes but the power draw is heavier and they're larger.
I think M0BPQ is likely to use it for testing with a CCW SDR given it is for RX only.
I'll report back on any developments / system overheads etc when signals are being received. I've just been setting up the box and APRS Messenger and VNC software. I'll be handing it over on Friday.
Not sure if this might be a portable option for someone if they're carrying a 5200mAh LiPoFe and can use a converter to get a stable 12v.
Anyhow, just wanted to conclude what I had found.
I am following the Fldigi stuff with interest.