You know engines often have third party dependencies right or the have their own built in stuff?

You do know that godot is open source right, all the machine bits exposed? No need to even do decryption and reverse engineering, to plug and change it to your method.

I latched on that you want to do cloud, except I cannot get a good definition from you on what you want to solve with the cloud. You say it is cheaper, but I point in running cost cheapest is to not host at all? I say you can build your own especially with open source. Basic principles on what your game need should answer quite well weather you need a "cloud" (Need to get what your definition of this is)

between utilising some kind of expandable cloud service versus allowing players to simply make and maintain their own servers, versus LAN.

With make you seem to suggest that they cannot host themself? What difference is that then from the cloud? otherwise what difference is it from LAN?