It's a pretty safe bet that they will not update the firmware. The 321 is not part of the current product line per D-Link's web page even though it looks like you can still buy it on-line. So unless they have to fix some major security hole that comes up in the future, I wouldn't hold my breath for any more updates. What you see is what you get.
Edit: I just noticed your post from earlier this year. IMHO, D-Link is working the low end of the NAS market with decently-priced units that are supposed to work according to the specs that they were designed to...but without a lot of post-sale updates. That costs money, which would result in higher prices. If you look at the high end of the NAS market--Synology, for example--you'll find they incorporate whole lot more functionality out of the box, and their strategy is to keep all of their products on the same update release stream until they simply run out of processing power. But this costs more $$ to do...more capable hardware in the boxes, more money in support. Which costs at the cash register. A very different approach than what we see with D-Link.