by using an alternate delimiter like q{} or q// the problem is just postponed

Postponed until when — the unlikely event that all possible delimiters also do occur within the string itself?

For most practical purposes, this likely wouldn't be an issue (or less of an issue that having to remember to take care of the special cases \\ and \<DELIMITER>).  And in those remaining few cases, you could still resort to concatenation, as you're saying.

But why write silly things like '$string=' . q{'} . '}' . q{'} as long as can simply say q|$string='}'| ?

That said, I personally don't really have problems with the way it's implemented currently.