Ugh, (c) should be:
"(c) stuff that uses wgDeferredUpdateList does not do (nor defer) updates when in
cli mode. Callers would have to do whatever themselves (which could lead to
duplicated code)."

(a) seems like a good solution: https://gerrit.wikimedia.org/r/48412

If anybody thinks (b) or (c) would be preferred then I'll abandon that patch.

Well that makes sure they are done, but it doesn't deal with the array bloat problem (which really slows down as the array gets larger).

It might help to use a wrapper function instead of just $wgDeferredUpdateList[]=stuff. Then would could have an option (d) where it starts doing some updates if the list is too big (in cli mode).

Agreed, but at the very least that patch is a good first step. I mean, it's only natural that a maintenance script should commit deferred updates upon exiting the script.

Change 211881 had a related patch set uploaded (by Aaron Schulz):
Avoid OOMing on deferred updates in CLI mode

https://gerrit.wikimedia.org/r/211881

Change 211881 abandoned by Gilles:
Avoid reaching OOM via deferred updates in CLI mode

Reason:
Already merged as part of Iff6625ddc04a15751d2bb07dc6558145e7ceb14a

https://gerrit.wikimedia.org/r/211881