Yes. At the very least some kind of pub/sub interface? Also worth noting that, if it's the data depth issue that's looking to be resolved, the Algolia API is often useful in places the Firebase structure falls short.
If you mean the documented API, it shouldn't be hard. If you mean reimplementing Firebase, that would be another matter.
Id do the opposite, Id build the new json stuff on top of the firebase api.
Just keeping the old API functional for its clients, really.