• https://en.wikipedia.org/w/index.php?title=Special:Contributions/Beyond_My_Ken&offset=&limit=5000&target=Beyond+My+Ken
• https://en.wikipedia.org/w/index.php?title=Barack_Obama&offset=&limit=5000&action=history
• https://en.wikipedia.org/w/index.php?title=Special:WantedPages&limit=5000&offset=0

In each case 5000 is the maximum accepted value of limit, and any higher value returns 5000. This includes the user preference setting Number of edits to show in recent changes, page histories, and in logs, by default (actually on enwiki the latter is now capped at 1000, hmm. On my home wiki with MediaWiki 1.27.4, I can increase it to 9223372036854780000, although such input is still interpreted as 5000).

IIRC this situation has existed since at least 2004, with no discussion of (broad-based) improvements to hardware and network administration tools in the meantime.

The use case for longer lists would be something like an internal corporate knowledge management system. Page/revision tables might become large, but few queries would run at any given time. End users would furthermore be accustomed to waiting, say, 30-300 seconds for a page to be served (from their experience with bloatware desktop apps and commercial cloud portals). Every so often, a huge set of pages would need review: legal discovery, regulatory audit, technical debt remediation.

Obviously such a limit would never be raised from its default on WMF projects, where volume always seems to increase to meet capacity :) and be accompanied by a sulphur-and-brimstone comment in DefaultSettings.php about the risk of DoS attacks and such.