This suggestion worries me. One of the best things about SO is that we don't have the RTFM and lmgtfy mentality found elsewhere. Namely because you're rewarded for the effort of finding and citing the relevant part of the manual. A built in RTFM tool will likely introduce an RTFM mentality in the SO community SO.
I also thought that one of the goals of SO was to be self contained, i.e., the answer to any SO question should be found within SO. External links breaks and contents of pages such as Wikipedia changes. Old answers with broken links are pretty useless and those aren't uncommon on SO as is and this suggestion, as it encourages external links, risks making that problem worse.
We're already encouraged to downvote trivial questions with no research effort and most of the general reference questions have already been asked, so new ones should in addition to being downvoted also be closed as duplicates. This has the same effect as closing it as general reference, except SO is still self contained.
I really don't see what value closing as reference would add, except it's easier to find the reference than finding the duplicate. A very simple way of making it simpler to find the duplicate is to mark the question as a general reference question and close it as a duplicate of the original general reference question. This way the general reference questions get closed without introducing the RTFM mentality in the community.