While designing tables for categories, I hope that some thought be given into implementing category intersection. I suspect the process would be much faster with properly designed tables. In previous discussions, the server load needed to intersect very large categories with little or no common members was enough to prevent the implementation of category intersection. At the least, if there is a count stored with each category, it would be possible to limit category intersections requests to categories meeting predetermined size requirements.
There are some other upgrades for categories that might also be considered at the same time. One frequent request is that maintenance categories not appear in pages with the other category listings. This would require a flag in the category table that could be set somehow, or perhaps with a new type of category name space (mcategory? wcategory?)
Samuel Wantman en:User:Sam