Firmware upgrades, absolutely. They're essential to any modern piece of equipment. The main CPU has both USB and Ethernet interfaces.
As for DLNA, I don't know where I'd do the A/V decoding. The CPUs in the platform are pretty much accounted for, I'd have to add another chip just to handle that. Plus, it feels like something better accomplished by a device designed for the task.
I thought about it after I asked it and came to the same conclusion. I figured it wouldn't be something you'd care to concern yourself when anyone could just get a player of some kind that already has it. Still, some of your ambitions regarding this project have surprised me.