If a user currently wants to set color (P462) to magenta and types in magenta, the first result that they currently get is the Italian commune Magenta (Q42595) and not the color magenta. The user needs to read the item descriptions to find the correct magenta. For experienced users this is extra work to do. For new users, it makes it more complicated to understand Wikidata then it would be if the Italian commune would not be shown in autocomplete for color (P462).

Currently, the one-of constraint is taken into account while showing autocomplete results but other constraints aren't. If value-type constraint and none-of constraint would be taken into account, the user experience would improve. While Wikidata has a bunch of other constraints as well, most of them are not relevant to filtering out hits in autocomplete, so the don't need to be considered.

For queries of 1-4 characters, the results of the query for a given property could be cached for a month to save database query cost.  

Any item that violates the value-type constraint shouldn't be shown. For items that violate the none-of constraint the replacement item should be shown instead.