That's a request that dates back to the legacy DNS-323 and DNS-321 models. 
Oh really? Haha, if you look at the android scene for example, CM has made leaps and bounds by adapting and fine-tuning google's original android codes. In a way that provided a lot of interests to the community especially in getting some useful but missing features up.
Code will always have bugs and we can accept it. If D-Link does not have the resource to maintain it, I'm sure the public domain do, at the very least the community can help out.
From a corporate point of view I do understand the reluctance from DLink side to provide visibility to the codes (DLink is reluctant to explain their firmware release lifecycle), but opening it to the public do have its benefit.
From the users point of view, at least we know that we are not left stranded
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Thank God that 2.03 was released before it went EOL, otherwise it'll be a black elephant lying in the corner of a room unplugged due to whatever files we copied into just get shredded to zero bytes.
I have yet to look at the product that supersedes the 320, but I do hope the USB port is now at the back rather than the front!