I see a problem with this not because people don't like it, or they will need to get used to it, or something similar.
I see a problem from devops/administration perspective. There are millions maybe billions of scripts/tools/automation written around these terms.
The change itself in software/repo is small, simple even, however what about tooling around that doesn't know about this change. What if every repo will implement these keywords differently (I've seen already roughly 5 alternatives for blacklist/whitelist)
Now imagine situation. You have a software and automation around that software. This software is responsible for breathing systems in a hospital. The server where it runs breaks, luckily it is clustered, but hey, the automation counts with master/slave, but now suddenly the automation broke, because someone updated the clustering software which already implemented the keywords changes.
There is a software that used --blacklist and --whitelist as a params, but now these changed to --allowlist and --blocklist and suddenly automation that counted with original keywords breaks.
And this is not even a big stretch of a situation, system updates might be automatic, or they might be done by separate team, so team responsible for automation might not know it.
This can have mild consequences, but it also might have a catastrophic ones.
If we can ensure that these changes can be really done smoothly without breaking important stuff, then yeah, feel free to do it, but can we really?
Honestly I think this is more a problem of whitelist/blacklist and master/slave. Changing the branch name might not be as risky, but if we are not careful with these changes, and will start randomly changing words used for decades, it really can cause some serious troubles, even lives.
Our jobs very often literally revolve around problem-solving to automate our own jobs into oblivion.
I'm sure we can manage updating our scripts or making aliases to transition. It's not like deprecation doesn't already happen all the time.
By the way, MongoDB moved away from "master/slave" ages ago. As has AWS, Microsoft (SQL Server), and several others. If you use any of the tools that have switched and haven't noticed, then it's probably not as impactful as you seem to think.
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