I would be interested in a downgrade (and lower priced as a side effect) of the DACPortable similar to the difference between the DACPort HD and the DACPort Slim.
The DACPortable has its own battery built in, a better noise floor (probably a side effect of having its own battery) and supports 24/384 and DSD. 384/24 is overkill for a device intended for mobile use. Most people can't tell the difference between 16/44.1 and 24/48 or 24/96 in ideal listening conditions, so they certainly can't in a noisy OTG environment. Chances are that if you're somewhere that you can appreciate the difference you're probably going to have available power.
I know (from the comments section) that there are plenty of people buying the DACPort Slim and using it with their mobile phones so It would certainly seem like the market is there for such a device. I would love to see the DACPort Slim made mobile. Same output power, same THD, same sample rate support, just easier to manage OTG. While we're at it, I could also go for a better means of keeping the cable plugged into my phone. Where I'm at now, if I breath on it it will disconnect and the must stops and I become sad.
FYI, my solution thus far has been to put my obnoxiously large extended battery (10000 mAh) case on my phone to drive my DACPort slim.