Before you go getting any bad ideas, know that Benninger and Sobell haven't released the app for public use, and warned both transit systems in late 2011 (though neither region has fixed the exploit, the duo claim).
For example, tax-gathering should be done at regional level, with the proceeds shared in fixed proportions, and the region, not Madrid, deciding how much goes to the town halls below it.
If the days of the cheap dollar and nearly-fixed exchange rates are over, the region also needs to find more dependable ways of managing its currencies.