Hi, I decided to have a go at this. A year has past since this post and the tools are a little more streamlined now, mainly that you don’t need to recompile Rust. I learned quite a bit. I have now produced a cross-compiled ARM binary of safe_vault. It contains a static libsodium and dynamic links to the glibc library, which is as portable as it gets for ARM on Rust, with current methods. At least I think that’s what it is… ldd does not correctly report the dynamically linking for cross-compiled binaries while they are on the host system - they need to be on the guest system to get that information. It was certainly built with a static libsodium library however. The “file” command does report that it is dynamically linked, so I’m reasonably sure that it is what I expect it to be.
I believe it is a drop-in replacement for the ARM7 Maidsafe release.
I don’t have access to ARM hardware at present, and creating a virtual machine under Qemu on Debian almost got me to the point of testing it but not quite, and I’ve run out of time.
So I would be grateful for someone to download it and play with it. Since the seed vault of community1 is currently participating in Testnet4, that isn’t available to test on. You might try attaching this safe_vault to Testnet4 or the stable droplet network. I’m sure you all will work something out. 
Please let me know how you get on.
It is here: http://91.121.173.204/armv7/safe_vault
Incidentally, an x86_64 (aka amd64) Linux version, suitable for any 64-bit Linux computer with an Intel/AMD CPU, is here: http://91.121.173.204/amd64/safe_vault That is 100% static linked.
I will shortly put up a number of these, being automatically built every night from the current repo. Next will be builds for 32-bit Linux, Windows and OSX. So people will be able to run the bleeding edge build appropriate for their systems, if they so choose.