Specialist notations can be accessed by making raw scores. It would also give more flexibility, which is often needed with specialist notations. Is there a problem with using <score raw?
The use of the raw parameter is recommended for music in uncommon notations. Using that attribute allows for more complex features and total control over the output, as nothing is provided. I do not think this merits an attribute of its own, as did T49604: Score should support note names in other languages.