It's definitely important to be thoughtful of MTA capacity, but FiDi is probably one of the best suited parts of the city to make such a change with minimal MTA

It's definitely important to be thoughtful of MTA capacity, but FiDi is probably one of the best suited parts of the city to make such a change with minimal MTA impact. You can start with parking spaces: even if those are mostly for commuters (which I'd be surprised to hear), and all of them stopped driving if we got rid of free parking (instead of paying for a parking garage), how many more MTA riders would eliminating parking create? FiDi is very small geographically (so not many parked cars fit anyway), yet it's serviced by almost all subway lines (so you can distribute the new load over many lines).