You are being sarcastic right? There are some incredibly complex systems out there where a huge part of the business logic is handled by these boring "servers and databases and real-time technologies" and where it would be inconceivable to try to offload this work to the client/browser. If you really serious, then you are also extremely naive. If you're just building an online collaborative text editor, then yeah, you can safely do away with this boring backend stuff.

As a side note, I think that firebase is an amazing piece of technology and I can't wait to use it.

Curious, what do back ends consist of if not code?

Semantics. Back ends are coded; it's just boring code. In any case, I can see this being useless for a lot of commercial projects if there is is no way to avoid data travelling outside your network. Or at least, that might make businesses apprehensive about using it.