How do you plan on doing your income scheme without having people enter their SSN at Fare Vending Machines? Seriously, no other place in the world charges fares based on a person's income.
If you want to talk distance traveled, like Berlin's ABC zones, I'd entertain that. You can go a long way on the T for a single fare. That's for sure.
Distance traveled would require all-new fare gates, since you have to swipe a card on both ends. It's possible that they planned ahead and bought gates with a retrofit capability.
You don't implement it at the vending machines, you implement this whole thing through monthly passes. It's possible that you could charge a high price at the vending machines to catch tourists and occasional travelers (not gouging, mind you).
Ultimately, your goal should be implementing a fare system that uses Apple Pay or some other RFID system to bypass the need for fare machines altogether. Then, you could limit the one remaining machine per station to single-ride passes. That's a long term vision, though.
Seattle's King County Transit is going to begin implementing income-based fares, based on qualifying for reduced fares based on enrollment in other social programs (i.e, KCT isn't reinventing the wheel).
This is a good place to start, but again, it places the burden on the low-income people to be signed up for one of these programs, and there are plenty of people that can't afford a $125/month transit pass that aren't on welfare.
My very rough concept:
1. When you first sign up for a monthly pass, you do so online or at a Charlie Card Store. You're asked to report your income range (low/med/high) and you're charged for the rest of the year until April 30th based on the applicable rate.
2. Then, with your MA income tax forms you receive an optional transit form. People outside of Metro Boston or who don't ride the T simply ignore it (or maybe there's an RTA version). If you have a pass, you write in your account number and elect to either renew (which just tells the MBTA to keep charging you at the appropriate rate) or pay an annual fee equivalent to 11.5 months at your monthly rate, pre-tax. That's a big chunk, but the benefit won't be meaningful to people not able to pay it, both because of their lower monthly cost and because their tax bracket negates the value of pre-tax.
3. If you don't send back the form, your subscription expires effective May 1st (there would be a way for people to renew after 4/15 a limited number of times, so that people who forget the form don't get booted). Each credit card number can only be used once to initially register. Some people will continue to open new accounts with new cards, but as with POP the losses will be minor.
4. For first time renewal, if you send back the form and your previous year's income doesn't match what you reported initially, you get billed for the difference on May 1st.
This isn't so different from how the RMV promotes and administrates EZ-PASS alongside driver and vehicle registration. In fact, if people get used to the tax form, the State could slap a VMT tax on there at some point down the road...
I have two concerns:
1) Raising fares on higher-income individuals could allow transportation alternatives (e.g. Bridj) to become more attractive to that population leading to under funded public transpo.
Bridj is looking to make money. If you raise public transit fares up to a point, they'll raise their prices. Uber has already demonstrated that effect.