Sometimes is necessary to move entire set of pages which are in tree relation, therefore it would be useful to make it possible in one step rather than having to move each subpage manually.
So I have idea about adding of "Move also subpages" checkbox to Special:Movepage, which would allow to move all subpages at once.
Version: unspecified
Severity: enhancement
I thought of the same thing some time ago. There are cons and pros for it. For example, checking that box when moving a page with thousands of subpages (like the RfAs on different Wikimedia wikis) would result in a high load of work on the servers. If, for any reason, one of the tasks couldn't be done (suppose that only one of the subpages is protected, and the user is not sysop) then we need a way to tell the script to continue with the others, show relevant warning messages to the user, offer otions, etc etc. That is a lot of work indeed ;)
Finally, I decided to think this is what bots are for.