It's not certain just when iOS 12.3 will arrive, although there have already been four betas as of this writing. A finished release may be a few weeks away, if not sooner.

Whenever it shows up, it would be part of a larger plan. Reported leaks claim that iOS 13 will support a much wider variety of mass transit cards, including different takes on cards that require loading value. It might just be a matter of time before your iPhone supports a local tap-to-ride service, whatever the format.