Would it be possible to search were a specific subfile is used?
In general - yes that is possible. In detail - no, that is not the purpose of LDFind. LDFind only uses the header data for searching a part. But you idea isn't bad. I have a name for that application already: LDStructure. :)
This could be my next project.
I want to know how many parts I've made.
Current version of LDFind can not do the job. But you are author of 217 parts in the library :)
Stay tuned ;)