Here in Berlin the idea floating around is to make yearly tickets very cheap (365€), while keeping prices for single travel (2.80€) or daily tickets (9.50€) more expensive. That's probably the easiest, least bureaucratic route to go.
For poorer households, the yearly ticket will still be subsidized, but the public transport companies (fully owned by the state) will still have direct income to maintain a corporate-like structure.
It would be much easier and less bureaucratic to just make it free and adjust taxes for residents and overnight fees for turists accordingly. Just the savings on all the ticketing and compliance systems and staff should be significant.
Considering that single travel tickets cost 3€ at the moment, and yearly ones 730€, that would be a godsend. One can also hope that one day they'll allow traveling on a single ticket for the full two hours, not just for one journey. However, it's unlikely the BVG will ever budge on pricing.
Earlier this year, there were rumors of a cheaper "Homeoffice-Ticket" which would only be valid on certain days, and in the end nothing came out of it either.
For poorer households, the yearly ticket will still be subsidized, but the public transport companies (fully owned by the state) will still have direct income to maintain a corporate-like structure.