I agree this would be positive. But the source only get's you halfway there though, you still need to actually be able to reproduce a compatible build system. And the longer ago the software was originally developed, the more challenging that becomes.

There are lot's of old projects out there relying on some ancient VS2003 installation. Same will happen with modern languages in a decade - code goes stale, and it get's more and more difficult to pull down the versions of software it was originally built with.