> and I've never seen it done by anyone else

In msg294174 Thomas says he intends to use it for Python at Google in order to "avoid third-party libraries even when they are available on the build system".

I do not have a strong opinion about this. Implementing the reverse configure option '--enable-custom-setup' is straightforward (actually this is what I did upon the first shot at this PR), Setup.dist becomes the default then and Thomas can still use Setup.local to add the *disabled* modules. It is annoying that there is no documentation on the build process that can be modified to describe the deprecation in details. Do you think a What'sNew entry is sufficient ?