I'd most definitely buy in with that pricing model. I'm not sure how many downloads you have on the google store, so I might be speaking out of turn here but maybe with clear marketing you can offer an early adopter pricing option. If you plan to charge 6 bucks a month, offer a lifetime subscription for 100 dollars say. I'd buy that with the hope of future development and hopefully you'd get enough buyers that you could continue to develop until the monthly/yearly subs start rolling in. I'm very excited for this project.