To be honest, relational databases are a pain in the ass to work with
IMHO. I've never come across any problem (trivial or non-trivial) for
which a relational representation is the natural one.
With respect, I believe that is at least partly because you have no experience with a proper functional implementation of the relational algebra. (Few people have.) Relational programming is another paradigm like structured programming, object-oriented programming, and logic programming, all of which Scheme can handle and handle well.
Relational programming in SQL, on the other hand, is like functional or OO programming in C: it is technically possible, but you keep running up against roadblocks placed for historical reasons that are no longer relevant. SQL is not only both too simple and too complex to do the job, it is full of idiotic limitations (examples on request). Unfortunately, it is all we have. Still, translating high-level languages to C has its good points, and so does translating high-level relational algebra to SQL as needed.
Following in the footsteps of Dee (a Python library for relational algebra), I think a good integration into Scheme is possible. It will not be an ORM, because mappings between paradigms always suck. But Scheme is inherently a multiparadigm language.