I don't see the point in a recovery partition. My Pandora travels in a carry case with SD slots and a couple extra SD cards, one blank, one with android stuff, and one with SZ 1.71 on it. If my stuff gets jacked, just pop it in and reflash. I would bet most people have the same.I had to boot of DVD twice - once to install the system in the first place, and once when my SSD controller broke, and I wanted to see what I'd lost and what I could still access. So far I've not needed to do it that often, so I've not looked into using USB sticks - in fact I used an old image I last used to set up an old desktop that only had USB1.1.
Debian's had plenty of remote holes in the last 12 months, although perhaps I am being overly pessimistic - provided you don't enable sshd, you don't have to worry about openssl holes and so on. When I recover my arch machine, I am using an image from 2013, which would have plenty of holes in it if I actually ran external services on it, but since I don't I'm not bothered.
Against the idea of a recovery partition, the thing I'm envisaging would just dump you at a terminal, so it wouldn't be that user friendly either. Perhaps it should also contain a simple shell script that would take an image off an SD card inserted, and use that to reflash the main partition. But is that actually any easier than downloading the image off the firmware website and unpacking it to and SD card - booting that will reflash the flash? Or are you envisaging a bootable partition that will just reflash everything with an old version of the OS and bootloader after checking that's what the user wants to do? That only really needs a select few services, and compressed rootfs and bootloader files, so shouldn't need all that much space. I could get behind that, if you're proposing to develop it.
Guess you missed notaz post. The image is about 1gb. You will have plenty of space. You still haven't said why your backup can't be on a microsd seems like that would work perfectly for you. I mean cmon we will have the potential to have 1.5TB worth of space (with all SD slots filled at 512GB),"Not that much space" adds up if you don't have any to begin with. With 16GB it would have to be a netboot image. Which is where new and old users will fall victim to not being able to connect to their Wi-Fi because they cant remember their key.
but you can only have a backup on the emmc?
You are really stretching now. Can't remember your key? Walk over to the modem, reset it and use the default password.
Next up: "But swordfish, what if you are cooking with hot oil and can't walk over"