> you still need to fix the rest of the stack to support split-off /usr. There's simply way too much code in our stack that assumes /usr was already there in early boot. And this is also documented in detail here: http://freedesktop.org/wiki/Software/systemd/separate-usr... -- there's also a non-comprehensive list of packages that are broken in this regard.
Not really: that page convinces the reader that there are attempted accesses to /usr before /usr gets mounted, but doesn't identify any actual brokenness beyond saying that the listed packages “[cannot] provide the full set of functionality” — which for all the reader knows might just mean e.g. that the relevant functionality isn't available until /usr is mounted (as I'd guess is the case for the locale example).
In LWN comments (but not in the above-referenced wiki page), someone was more specific and suggested that some USB network or audio devices won't be accessible with separate /usr unless they've been plugged in since /usr was mounted. Even if this example were added to the page, it's not very convincing if the only example offered is specific to (what the reader might consider or guess to be) rare hardware: the reader almost certainly has USB hardware that seems to work fine when /usr is a separate partition, so it might not even be that all USB audio or network devices fail to work.
For the reader who has a separate /usr partition and hasn't noticed the associated brokenness, the page isn't very convincing that separate /usr is broken, or that the brokenness of a separate /usr (that even that page describes as mostly “graceful failures” that “won't become directly visible”) outweighs the rationale traditionally given for separate /usr such as filesystem reliability (“all eggs in one basket” principle) or sharability.