Ole,
I'm aware that this doesn't exist at the moment but would it be possible to add at some point.
If any other Python experts has a view on this, it would be good to hear too.
For me the challenge seems to be speed. At the moment global search is still pretty slow on single words/phrases (when searching a large doc folder - in my case my nvAlt/Notesy folder) so to add boolean operators would probably hinder speedy response further without some form of spotlight type indexing service running too.
Now that IOS is a great document creation tool it seems to me that the next task at hand on IOS is a smart way of indexing those documents (local or cloud based) so that you're able to get a Devonthink Pro desktop style search experience. The Devonthink team made a hash of things with Devonthink To Go, so I wonder if something could be built into Editorial at some point in the future. It would seem that this type of feature would need to be built natively in Objective-C as a scripted solution via Python would probably be far too slow.