This isn't my idea at all, I am taking this from the way in which jQuery libraries are obtained.
I feel it would be beneficial to all of us if whmcs were to implement a download management to allow us to download only the sections of the installation that we need.
As a part of this, the core files should be standard with other things being selectable to compile a download per user. In this way we can choose which registrars we want, which gateways and any other such addons that might be available.
If these selections are then stored on the users account they can be used for later upgrades to only download the required files for the specific installation.
In the long run i feel this will be of huge benefit, things like broken modules that are not even being used by a specific installation can be eliminated and save a lot of work on our end and on the support team.