It took almost two years for the original idea to come together: Godot Engine version 4.0, as well as 3.4 will have the full support for 64-bit files and computations. This means that instead of 2.1 Gigabytes, you will be able to use files up to 9.2 · 10⁹ Gigabytes in size.
Here is the GitHub page related to the update.
Also, thanks to the general support for 64-bit accuracy, the work of other aspects of the engine will be improved (mostly, in 4.0, I guess). For example, physics or positioning on huge maps, even on a planetary scale, will become possible. But this part itn't yet included into the build, so you still have a chance to review it or propose something.
Some competitors, where such a system is supported, consider the feature to be premium (for example, in Unigine it is part of the paid SIM-edition).