I like that! npm, Composer, PyPi, Homebrew.
It will be much smaller, but far more representative. Complete view of any given ecosystem there, and all repo/hosts used within it, unbiased by what software/hosts you know, and with no incentive to limit discovery (eg cost of preserving full repos, would be out of scope).
There'll be some hosts where you probably can't determine the software used or where the host is down, but that's a good problem to have!