I use saved queries on the PC to filter my music collection. Mostly I use this query:
%path% HAS "CD Rips" AND NOT %genre% IS "Game" AND NOT %genre% IS "Movie"

A support for such queries would be a really great feature for foobar mobile. The queries should be saved with a name (as seen on the PC).

Since I simply filter my music by genre, a quick workaround would be the following:
- Select Genre in the main menu
- Select unknown genre
- <Now the new part...>
- I click on something like "All artists" and can shuffle through all tracks.