Alicorns are possible through the Sorcerer bloodline of Unification, as early as level 3 if you start as a unicorn or a pegasus(and take wings or a horn then).
There are no rules, yet, for Zebras of Griffins, but there's also no reason for there to NOT be, either. This is something I wanted to get more into detail about in stretch goals, folding in more and more races as we go.
Here's what we have right now:
Basic, Pegasus, Unicorn, Sea, Changeling, Chaos Hunter, Gem
All horse types, as you might imagine. Some are even mix and matchable. You can be, for instance, a pegasus or unicorn changeling.
I just find it really cool/funny how far you guys have come since then and how Zebras, Griffins and more have been added to the system since. Also: