Hi Nicolas,
Although it is not possible today, but hoping to see that day, when Lilypond will include all kinds of notations. As a matter of fact, we are stuck in that part in Bengali Wikisource, where there are
books on music using a musical notation from India called Akarmatrik Swaralipi. I guess, this is true for many oriental music systems, which Lilypond has not included till now.
Anyway, there can be different musical notations for a single music item. For that reason, P518 can be a mandatory qualifier for this property, which serves the purpose to distinguish the notations.
Regards,
Bodhisattwa