Not being a FARR expert this may already exist, or there may already have been lengthy discussions about why it's not possible, a bad idea, or whatever... buuut, having said that, what about:
A keyword system to use a specific app to open the result of a search. Could be a suffix, e.g. "g query fx" would use Google to search on the "query" text and the application associated with "fx" (Firefox) to open the result when clicked on/invoked. You could then do "g query ie" and get it to open in ie, or "g query np" for notepad. You'd setup custom keyword associations with apps the same way you apparently can for search types and plugins. Obviously the suffix approach has problems, so maybe it could be an additional prefix, or some other modifier, and then there's the concern that not every result may be able to be opened by said app, but then if you know you're looking for e.g. an HTML file or web URL in your search, then it's reasonable to specify a browser to open it, even if other results come up that could not be opened by a browser - you leave it to the user to decide and deal with the consequences.
It seems like this could be fairly cool and powerful functionality...