Remember Sharlayans forbid by law the teaching of disciplines of war to outsiders. It's easy to think of them as peaceful teachers of knowledge, but they're not - they're isolationists who avoid having a hand in the outcome of a given war, even indirectly (by way of teaching one of its sides a new discipline). They would much rather stand by, watch thousands of people die, then write it all down. So although there were many classes available to foreign students, classes in astromancy were not among them.
If RDM is Sharlayan in origin, I strongly doubt lessons in it would be freely available to outsiders, either - especially with renewed hostilities between Eorzea and Garlemald. It'd place it in the same position as AST, where non-Sharlayan characters who want to say they know it need to have a strong justification for how they came into possession of a restricted soul crystal.
I kind of hope it's a fresh discipline, like MCH, that's being developed by Eorzeans. But I guess we'll see? I don't really know where I think it's likely to come from...
If RDM is Sharlayan in origin, I strongly doubt lessons in it would be freely available to outsiders, either - especially with renewed hostilities between Eorzea and Garlemald. It'd place it in the same position as AST, where non-Sharlayan characters who want to say they know it need to have a strong justification for how they came into possession of a restricted soul crystal.
I kind of hope it's a fresh discipline, like MCH, that's being developed by Eorzeans. But I guess we'll see? I don't really know where I think it's likely to come from...