What use does this have to WMF?
I think we make a lot of cool features that require JavaScript. And yes, it's not universally usable, but it's helpful to spend time on those things, because while they may not make Lynx [0] users happier, they'll probably make things easier for, e.g., people who upload a lot of files [1] or who want to switch between languages more easily [2]. People who want to log in with a central identity and don't like using Google servers seems like a pretty OK group of people to encourage.
This isn't to say that it's not worth discussing--it definitely is, and we should keep our minds open to every possible answer. Daniel, if you disagree with the above, more information would be very helpful :)
Also, implementing BrowserID would pave the way for OpenBadges [3] integration, which would be _really_ cool.
[0] https://en.wikipedia.org/wiki/Lynx_%28web_browser%29 [1] http://www.mediawiki.org/wiki/Extension:UploadWizard [2] https://www.mediawiki.org/wiki/Universal_Language_Selector [3] http://www.openbadges.org/