As a beast tribe to add quests for, I'd put them in the bottom of my want-list, with Kojin barely edging them out.
Ananta and Qiqirn would be the top two to add quests for IMO (and maybe a Qiqirn primal, finally?)

Though Namazu do have an obvious choice for a primal; the... well... Namazu. Giant catfish that causes earthquakes. Guess they could make it 'mud' themed or something to avoid trampling on Titan/Leviathan.