I can't remember the exact reasoning, but essentially it's because they're something new. They have some of the advantages of a Primordial- Charms for everything they're likely to want to do- as well as access to other Yozi Charms.
There is still a way Holden pointed out to get the [You] Cosmic Principle Primordial into existence. Once you've got Flame of the Risen Phoenix, go and die- and your Exaltation's next bearer can race the age thing to get to Essence 10, never take Devil-Tiger (but still have access to your Charms), and learn Cosmic principle.
I'd love to play in something like this as well, but I also agree that it would be a hell of a lot of mechanics to wade through. Might I make a suggestion? Give everyone Triumphant Howl of the Devil-Tiger for free, but limit them to only their own General charms before play starts. It gives you a template of what those charms should do, rather than throwing you straight into the depths of homebrew.
And perhaps a very slow ascent along the new Charm tree so as to get a good feel for your own theme and details. And then and only then after you've figured such things out may you progress along that tree.
Count me in as heavily interested, this game sounds fun. A slow ascent up the charm tree sounds good to me. Sol Invictus knows that it usually takes a bit to get a good handle at how your character actually interacts with the others anyway.