At the beginning of next cycle we aim to merge the option refactor branch. This is a huge change that will touch pretty much all code.
The main change it brings is that you can override any builtin option value for any subproject (even the top one) entirely from the command line. This means that you can, for example, enable optimizations on all subprojects but not on the top level project.
We have done extensive testing and all our tests currently pass. However it is expected that this will break some workflows. So please test the branch when it lands and report issues. We want to fix all regressions as soon as possible, preferably far before the next rc release.