One of the most interesting (and maligned) parts of the Descent MK2i is the sonar connection to the transmitter. Obviously some people hate this system because it's proprietary or they notice a sound from the transmitter. One of the best things about it though is connecting to another diver's air as well as your own. My gf is a new diver, and I bought a second transmitter just so I can keep an eye on her air, we have yet to use it, but I am looking forward to seeing how it works. I trust her diving, and maybe it's just the nerd side of me enjoying having more data... but I also like the idea that I can keep an eye on her air.
So what else can be done using this sonar tech? It seems like a lot of potential. Maybe instead of just seeing your partner's air, you can see their NDL time too? Or get alerts when they are close to NDL or other limit? What would be really cool is a way to communicate, or at least send an alert to your partner... something like the old "Buddy Watcher" system. I could see where if my buddy sees something cool they could select to alert me of it... or there could be an emergency alert system too.
Obviously the interface for this would be important. You don't want to confuse the NDL of your partner(s) for your own. I also don't want to get an alert every time they ascend too fast... unless it goes on for 30 seconds... or some other user selected time. The communication should be intuitive and non-invasive. Perhaps a double press on a button sends a "hey, come look at this" alert to your partner, and a long press sends a more emergency style alert to everybody in the area.
Does the technology have the capability of locating someone? Scubaboard is full of "diver lost" situations. Maybe the ability to ping your partner could yield a direction and possibly distance?