Smart crates have some good options, but when we are limited where we can put data it keeps smart crates from really reaching their full potential.
Yes, comment and grouping can help when using "contains" in smart crated, but some apps are using those areas already to assist with other functions.

Smart crates need to start with boolean functions of "and" or "or" that can be groups. Rather than the options of all "and" and all "or" that we currently have.

Combine that with custom tags and rating and the smart crates would be amazing.
We need tags where we can mark music with multiple attributes like Acapella, DJ Tool, Halloween, and Clean all for the same song.
The rating of the music is also vital, especially something that could be edited quickly during a set so you can remember those bangers that really got the crowd going! Also useful when you are quickly going through music and want to be able to group those that you really liked for the set you are creating.
Either 1-5, or 5 stars or similar.

Smart crates are one of the great features in Serato, but they are currently hamstrung by lack of features supporting them.