Supporting the view that cantrips and racial abilities do not count as an Arcanum (for rules purposes) is the Primer. Important definitions bolded.
Primer pg.45 wrote:
If you are a spell caster you may not utilize either the Magic Initiate or Ritual Caster feat to learn spells from an opposed Arcanum (arcane, divine, or primal) of magic. For example, if you are a wizard you cannot take Ritual Caster to learn divine rituals.
Choosing these feats also restricts your multiclass options. If you choose to learn a divine spell and cantrips though the Magic Initiate feat you are no longer able to multiclass into any arcane spellcasting class or take an archetype which grants arcane spell casting.
It appears that characters are not locked until they take one of the classes listed on Pg.45 or either of the above feats.
Encali still can't take Druid, Ranger or Warlock (Spirits Patron) due to racial restrictions.
val'Mehan are still a (conceptual) problem but they don't actually get the Ritual Caster
feat for their blood power, working around the listed Arcanum restriction. However, if they are not taking Sorcerer-Priest as their source, the PC should be burned at the stake as a heretic anyway.