Proposal: Given a root wiki page, display a list of subpages for the given root wiki page on the deletion form and allow to check/uncheck some/all of them to be deleted with the root wiki page as well.
Rationale: Currently deleting a page with a large number of subpages is very tedious given that you need to open each and every subpage and perform an individual deletion. While this can be achieved via scripting or a bot, this is not affordable for all wiki administrators out there, so we should make MediaWiki to support this option by default.
Notes: probably deletions should happen in batches, not all at the same time, to avoid stressing the databases too much.
Similar to T32893: Add option when deleting to delete all subpages and option to delete all redirects. However this task aims to be more selective, considering that this one requests that MediaWiki let you choose what to delete and what not, not delete all subpages in a all-or-nothing fashion.