I think Ask Ubuntu does exist only for the shake of canonical (the company behind ubuntu). It is definately under the scope of (and hence the duplicate of) Unix & Linux. Unix & Linux misses many useful question because users of Ubuntu prefer to post on AU instead if U&L. Especially command-line, shell-scripting, text-processing, package-management etc are which U&L deserves.

So, Ask Ubuntu should be merged into Unix & Linux which is the world for unix-like operating system.

Or at-least I'm requesting to post a page at the help center or meta of AU to encourage users to post their non-ubintu_specific questions on Unix & Linux.

Thanks.