I have not seen or used the app. Having the labels in non-English languages can be very helpful. Typing vernacular languages on keyboard with just English alphabet is complicated to say the least.
If online verification is used, issues of no-connectivity/poor-connectivity/latency can cause problems. Polling units are sent to remote corners of the country.
Loading the polling unit with aadhar database can be one approach. Very few know (relative to the number of personnel involved in the polling process), as to which polling unit will go to which polling station. Trying to load constituency specific database into polling unit will increase the surface area of the people who have to know which unit goes where. Loading the aadhar database of full constituency into polling units might not be technically feasible.
To go slightly off tangent, will it make sense for Twitter to enter into the micro payments landscape? All (almost?) bloggers, people working on open source projects have twitter account; even if they don't have one, creating one is easy. Donors can get some kind of acknowledgement on their (and receivers) twitter feed and the content creators will get some money.
This year they have come up with something called netbanking verification. With that you don't have to mail any documents even if you don't have digital signature. If I remember correctly, there are other means of verification in addition to netbanking.