@Ivan Gretsky GitHub is a requirement for modules that are automated with regard to automatically pulling version and readme, etc. If someone needs a case where the module can't be managed at GitHub (like a commercial module or other specific case) then I would just ask them to contact me so I can add it manually.
I feel it's safest for our users by having downloadable modules provided by GitHub. They have security measures in place that give me a lot more peace of mind than a link to a random ZIP file off on some site none of us know. Without GitHub as a middle man, I think there's a much higher probability of getting something questionable in a ZIP file, whether it's because of a hacked site or any number of other reasons. GitHub also provides great security options for protecting individual accounts, which I think further increases the safety for consumers of ProcessWire modules.
The other side of it is that GitHub provides an API that we can read data from in order to ensure our module information is up-to-date and that users don't have to manage that information in more than one place. That API also includes a function to safely convert GitHub-flavored markdown to HTML, which is very useful for the modules directory. Presumably it would be possible to also implement this for other providers (GitLab was mentioned), so if there's significant demand for it then it would be worthwhile. But it took me a long time to implement the GitHub integration as it is, and at present I likely couldn't afford the time investment to implement another different API right now. Down the road I'm open to adding support for more Git providers. For now though I had to work within the bandwidth I could afford to devote to this project.
@Mikie
The module class name is used throughout, but it's true it doesn't literally say "class name:" anywhere. I think you are right it would help with clarity if it does that somewhere, so I'll plan to add it. As for version compatibility, I'm going through all of the PW 2.x modules and deleting any that aren't 3.x compatible and don't look like they will be. This will take me a little while, but basically the intention with the directory is that you can assume it's 3.x compatible. For more fine grained detail on version compatibility, it's going to read the module info array. It doesn't report that info at present, but this project isn't fully finished yet so it will be reporting more from the module info array in the coming weeks.