Yes, I think that it is good that they did not touch existing projects. (Much of the complaints (including my own complaints) when it was announced were due to ignorance of the working of git and of GitHub; once I learned how it is working then I do not have complaints about it.)
Even for new projects, if you create a empty repository on GitHub and then send a repository from your own computer, it will work with whatever branch name you give it, at least in my experience (I had sent repositories with the only branch named "trunk" and it seems to cause no problems at all as far as I can tell).
Neither git nor GitHub software cares what the branches are called as far as I know; I think they just changed the default settings if you are creating a repository using GitHub, but you are not required to use them.
And, actually, I read the documentation and you can even make per-user settings on GitHub, and you can change the default branch name for git itself too (and, like in GitHub, this setting can also be changed in git).
They also added the function to rename branches (you can rename any branch, not only the default branch), and they provide documentation about how this is working, so this is a side benefit of their work on this, in case it is sometimes useful to rename branches (although I think probably it is usually better not to rename existing branches, maybe sometimes it might be useful).
Furthermore, "main" is shorter than "master", and starts with the same two letters; but in my opinion, these are minor benefits (although they are still beneficial anyways).
However, even though I think this is good, this does not imply that all software that used "master" and changed it, were doing good. In many cases they weren't good, but git (and GitHub) isn't one of them that isn't good. The reasons why it is good or not good have to do with the existing working of the software and of working of names, and how the changes are being handled, and is not because of racism and stuff like that.