Recently a lot of people have been talking about what's possible and what's necessary regarding MediaWiki, CatScan-like tools, and real category intersection; this mail has some pointers.
The long-term solution is a sparkly query for, e.g., people with aspects novelist + Singaporean, and it would be great if Wikidata could be the data-source. Generally people don't really want to search using hierarchical categories; they want tags and they want AND. But MediaWiki's current power users do use hierarchical labels, so any change would have to deal with current users' expectations. Also my head hurts just thinking of the "but my intuitively obvious ontology is better than yours" arguments.
Conversations have been a bit scattered:
https://meta.wikimedia.org/wiki/Beyond_categories
http://lists.wikimedia.org/pipermail/wikidata-l/2013-May/thread.html#2202 ("Question about wikipedia categories.")
https://en.wikipedia.org/wiki/Wikipedia_talk:Category_intersection#A_working...
CatScan, which can find articles in category intersections: https://en.wikipedia.org/wiki/Wikipedia:CatScan
http://lists.wikimedia.org/pipermail/gendergap/2013-April/003552.html
https://bugzilla.wikimedia.org/show_bug.cgi?id=5244 "Allow searching in intersections, etc. of categories"
I think the best place to pursue this topic is probably in https://meta.wikimedia.org/wiki/Talk:Beyond_categories . It's unlikely Wikimedia Foundation will be able to make engineers available to work on this anytime soon, but I would not be surprised if the Wikidata developer community or volunteers found this interesting enough to work on.