Since Godot is MIT-licensed (which only requires a copyright notice and a note that says 'this is using code from a thing under the MIT license') changing the license would be trivial.
Essentially they could release "Godot current+1" under a fully proprietary (or GPL for that matter) license and keep the notice that's required by "Godot current" and they would be compliant, since "Godot current+1" would be a derived work from "Godot current".
The requirement to get consent from all previous contributors only applies if they would want to remove that copyright notice. For sofware that is under more restrictive licenses, like GPL, further restrictions apply and then it would be necessary to get an ok from all copyright holders to change the license to something that is incompatible with the GPL (or between incompatible GPL-versions, like GPLv2->GPLv3).
edit: While it would be ok to do this change from a licensing perspective it would of course most likely piss off quite a lot of the current contributors who didn't agree with the change, and they would most likely move to the aforementioned fork that would get started immediately.
Essentially they could release "Godot current+1" under a fully proprietary (or GPL for that matter) license and keep the notice that's required by "Godot current" and they would be compliant, since "Godot current+1" would be a derived work from "Godot current".
The requirement to get consent from all previous contributors only applies if they would want to remove that copyright notice. For sofware that is under more restrictive licenses, like GPL, further restrictions apply and then it would be necessary to get an ok from all copyright holders to change the license to something that is incompatible with the GPL (or between incompatible GPL-versions, like GPLv2->GPLv3).
edit: While it would be ok to do this change from a licensing perspective it would of course most likely piss off quite a lot of the current contributors who didn't agree with the change, and they would most likely move to the aforementioned fork that would get started immediately.