How about an “advanced/basic” toggle that lets users enter their own SQLITE query directly? I’m really fond of this feature/UI in the Atlassian JIRA bug tracker software which you can see it in action at https://jira.atlassian.com/issues
Your existing easy-to-use syntax can stay as-is, but users wanting more unique/advanced queries don’t need to install separate software or wait for you to consider implementing it. For example for Search for single KW (exclusively) and Search by color
And if some requested item is not already indexed, I assume it’s less work for you to add a new PhotoStructure | PhotoStructure's advanced settings that adds such-and-such to the index without additionally immediately having to decide the plain-language syntax. For example the duration column you consider in Please suggest other search examples - #23 by mrm, and the columns implicitly suggested in the previous links for number of people and for color name.