I have a Dev Alpha "A" as well as a Dev Alpha B running the full BB10 OS (vs. a limited developer build).. The Dev Alpha B is basically a "London" device inside a plastic disguise case (but with only 1G RAM vs. 2G for the retail device), whereas the "A" was mostly a Qualcomm reference design in a Playbook-like case (again, with only 1G RAM). What this means is that the London loader files will work with the Dev Alpha B and turn it into a fully functional (3G/4G wireless) BB10 device; parties in the right Beta programs have access to the full BB10 loader files for the Dev Alpha B. Now as for the "A", as far as I know, other than RIM insiders, there is no public access to full BB10 loaders for that device, but you can install the London loader files onto the "A" (no, it won't brick the device, at least not the older loader I used), which will give you a 90% functional device (WiFi only, 3G radio won't work), but there's actually a relatively simple procedure you can perform after this that will "fix" this situation and turn the "A" into a fully functional device (3G wireless only, as this device doesn't have an LTE radio, *BUT* you still need a LTE-compatible UICC SIM card to make it work).
I believe part of the reason I believe RIM has not released "A" loaders is probably that this device has never been certified for most carriers and I don't recall if it had FCC or other government approval numbers on it, the second reason is that with only 1 Gig of memory, neither the "A" nor the B have enough RAM to run at its best with full multitasking, etc: I crash apps on a much more frequent basis on the Alpha devices as the run out of memory, and in particular, the "A" is noticeably slower, which is probably the main reason why RIM is keeping these devices as developer test devices with stripped down OS to maximize the amount of free RAM..
<I'm Joking><Seriously, I really am joking here> If a Dev Alpha goes for $1000, I've got a Dev Alpha with full BB10 here, and it's got to be worth more than with the stripped down OS right? It's BB10, so it's got to be worth 10x as much, so first person to bring me $10,000 US cash offer takes it... Small, unmarked bills only ;-) </Seriously, I really am joking here></I'm Joking>