Right now I am in the process of manually mapping out three 1400-3000 mile loops I plan on tackling over three different upcoming summers and have been seriously considering using a GPS unit for assist while riding, but don't want to have anything more than my phone with me. I like the ideas you have presented and I think it is worth pursuing. Voiced directions are a great idea, however having a map display is essential.
How about picking up where Pedalcell left off and produce a rim powered power unit to keep the phone running while in use? I bet you know someone who has the engineering skills for that project. Then I can use your phone app alongside my handmade maps!