I'm glad to hear this. Over time the amount of work me, my colleagues, and my graduate students do on an iPad as opposed to the desktop has increased. At first it was just reading PDFs, but now we find ourselves doing a lot more. It is at the point about now where several of us have gotten rid of our laptops. Sure, we still do "serious" academic writing on a desktop computer, but when we go to a conference or on a short trip, an iPad (sometimes with a bluetooth keyboard) is "good enough." I expect this trend to continue, even accelerate.
The lack of a mobile interface or app is the main reason my colleagues have been unwilling to try Paperpile, even though I have been encouraging everyone to do so. That also means that the current Paperpile users are probably already self-selected from people for whom mobile is not that important. In my experience this is a rapidly shrinking user base.
I would also like to add that I think that there are many mobile usage scenarios beyond just reading and discovering that people use right now. It is common for academics to want to share and discuss papers via email and social media, or even in person, over coffee, and it is frustrating in those situations not to be able to quickly look up a citation that you have already carefully catalogued in Paperpile. For this reason, a read-only version with basic sharing features would be most welcome, (even though I understand your reluctance).