Single website that at /orgname will show the combined results in a way that makes it clear they may be separate orgs (so you can't really phish by grabbing /bankofamerica or something)
Same abstraction over search, repos, etc
Support popular services like gitlab, github, bitbucket, etc
If sites used semantic metadata to markup what's on the page - and each site would have its archetype - github has issues, repositories, organisations, you could make a generic site coalescing frontend which aggregates sites in general.