My issue with constraining shapeshifting to animal stuff is that the theme of "animal stuff" isn't very interesting. Animal stuff gets you 2E Lunars, where you had "get more soak, but for animal reasons" or "be cunning like an animal" or "get an essence weapon, but its claws!" You can get cool powers out of it, but it it feels (to me) shallow. It's stuff I've seen before. It's stuff my D&D Druid was able to get. Broadening the theme to "shapeshifting [acquiring via stealing the metaphorical and possibly literal skin of your target]" where you are capable of turning into basically anything other than an Exalt feels deeper to me, outside any mechanical considerations. It feels more like something I can design Charms for, across all Essence levels. It feels more like a statement about what Lunars are supposed to
do with their powers, what Lunars are about. They're Alex Mercer, or Megaman. Getting new shapeshifting forms is interesting gameplay, it's stuff that motivates plot. You want to be out hunting the biggest monsters. You want to be slaying [the things that happen to be the enemies of Creation], because that gives you power. It makes Lunars scary, for the rest of Creation, especially the powerful, who think that they're safe behind their walls. It makes for interesting internal divisions within the Lunars, about how far they're willing to go for that power.
It makes Lunars more interesting in the setting. The Tell, if that's coming back, becomes really important. That random God? Could be a Lunar—you don't know, even if they're using clear God powers. That Blood Ape you summoned? A Lunar killed and replaced it. Only fellow Dragonblooded can be trusted without thorough examination, because only their talents cannot be stolen and mimicked. Lunars become broad, able to master a hundred tricks. Picking up strange, different forms becomes something valuable, because you're getting real value out of that.
I think
@Omicron's concern about this encouraging Lunars to immediately go for magical creatures and never look back is real—I could imagine a number of ways to balance it out, from extra mote (or even wp) costs to assume magical forms, xp costs to acquire them, charm-gating access, Charms that only work on mundane forms, your Anima coming out quicker in a magical form, etc., but I'm not sure how desirable some or all of these would be. I do think that there's some balance space where the Lunar who wants to focus on mundane forms isn't overshadowed by the Lunar who goes straight for magical ones though, although given that the devs chose to go another way we'll likely never see.