There were certainly sites that used /u for what is now commonly /home (or /export/home on Solaris, /Users on OS/X, ...) This was not something that predated "/usr" though: /usr was already added back in the early 1970s (the linked article was correct about that, although it got many other details wrong)

Basically /usr was originally only for home directories (as the name implies) Then it became the place for anything you didn't want to use the precious space on the root filesystem for (hence /usr/bin popped up, and later things like /usr/dict/words) Finally, it became so cluttered that people started locating home directories elsewhere and now the name "/usr" is completely unrelated to its actual purpose.

I wonder if this is the origin of the 'bin' user as well, because that's a design decision that never seemed to make any sense.