At the moment github has got one of the least complicated set of terms out there. If Microsoft take it over then those are going to change, which means that thousands of end developers are going to be asked to sign up to something to carry on doing their job.
In effect thousands of employment contracts are going to get unilaterally modified by a third party.
If those changes are materially detrimental, for example Microsoft may run "telemetry" and share the results with "partners", then I'm curious what the legal position is.
Welcome to the world of SaaS.