In my case, when I start setting a new development environment, I always forget to install some development dependencies, and therefore quite a lot of modules fail to configure/build/install. With a new option, kdesrc-build will only retry the modules that failed, making the process a little bit faster.
This is already implemented, see the --rebuild-failures command as documented in the kdesrc-build man page and Docbook manual, added a couple of years ago with commit 51c3a7ec5. I ran into the same issue you described often enough that I had finally added this for myself... On the other hand, if this command isn't working then please reopen as a bug. ;)