Damn, I would love this. Student UPASS (universal bus pass) for my city is roughly $80 for a 4 month term. It's less than half the price of buying monthly passes, because it's a non-refundable, non-negotiable fee. Every student at both universities in town pays it.
According to recent financial statements, oeprating costs for 2015 were $80M, with fare-box revenue of $33M. In a city of 500,000 residents, our public transit taxes would have to go from $94 per person to $150 per person to make it free to use all of the time (modulo increases in costs due to higher use). That's like, the price of taking a date to the movies and getting popcorn.