I understand the change from master to main is going to throw people off merely because of how used to master we are regarding version control. While the word master doesn't have any intrinsic meaning when it comes to versioning (since there is no slave to it per se), there are concepts where it does make some sense.
Professionally I work in pro audio - I am a sound designer for video games, to be exact - and the master/slave relationship actually does make sense as a concept there, since you can have an audio workstation (i.e. Logic Pro, Pro Tools etc.) dictate the general settings of the project to a slave workstation that just inherits the master's timeline tracking, I/O settings, timecode and so on. While I don't think the reference to actual slavery is even remotely significant as to justify a change in wording, should a better or equivalently descriptive word-duo appear I would be all for it.
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