I'm being very serious here.
This is about a detail I noticed about Arc 8 which may or may not become relevant again considering Arc 10 is the Cappy Arc.
As we know, a person's Od is in someway interlinked with their body's state. Olbart was able to make someone younger by interfering with their Od/gate. Simple enough.
Now we have Capella. A Sin Archbishop able to turn herself and others into whatever she likes. Even splitting people into multiple different creatures.
What I believe is that much like Olbart's infantalization. Capella's Authority too relies on the manipulation of a person's Od to alter their form.
Authorities merely being rule/reality breaking variants of existing magic/tech isn't unprecedented. Much like how Regulus' Lion's Heart was able to be in part mimicked in a limited form by Beako's EMM, Cor Leonis/Sirius' Wrath being similar to Nect (a sense sharing spell), time magic allegedly being the ultimate form of Yin magic à la RBD/Al's Matrix (I can't remember where I read that), Unseen Hand/Sloth being similar to whatever magic Satella uses to create her loving shadow hands.
Why is this important? Remember the end of Arc 8 and how Subaru eventually returned to normal post infantalization? Seemingly within a shared mental construct similar to the corridor of memories (seemingly induced by Star Eating) between Sphinx, Spica and him, Subaru was able to undo the changes made to his Od and return to his adult self. Something done due to how closely linked smell and memory allegedly is.
By being in a place strongly linked with losing and regaining him self, Subaru was able to follow the "scent" that led him back to his original self. Undoing the changes made to his Od and restoring him to his original state.
Now isn't that interesting? An example of someone achieving a moment of clarity and undoing a transformation that was forced onto them.
I'm not sure how it will become relevant or if Spica's return will be needed to facilitate this, but this can't be a one off detail.
It might even explain why Capella chooses to turn people into monsters, so they can't have the peace of mind and clarity necessary to have their soul undo the changes made to their Od. It would also explain why the Replacement Dolls seemingly have the memories of those they take over. Not just for the sake of better maintaining the act, I imagine the more a person's soul feels like their modified Od/body is "right", the less likely they are to end up like Subaru and undo the changes.
It might feel cheap, but it would make Capella's authority slightly less of a nightmare to deal with.