If you're referring to knowing exactly your balance, I'd guess with a phone payment app (e.g. Apple Pay/Wallet/Android Pay/whatever you want) you'd be able to see, manage, and probably refill your balance on the go. While using an eventual OMNY card might not allow it, the general assumption is that people will use their phones for most of the payments anyways, and cards will be less common. In that regard, I think that opens up more possibilities than both tokens and the MetroCard, since you could easily manage your payments anywhere via your phone.