First off, it'd just be nice to have some options that go into the diagonal space above & behind the head. Since i ended up just having the one image showing both of these suggestions, I'll put it at the end.
The main thing though, is symmetrical ears. Like how wings is Symmetric Dual so it can use a single texture, being able to have both the left and right ear use the same texture (1 front, 1 back) frees up space so that with modes like Out and Sides you can have more space than 8x8, like 8x12 or even 8x16 if you want.

Also, an idea I had while writing this is being able to make the tail texture longer. It'd be a bit more troublesome since it'd necessitate shifting some areas around, and chopping up the tail texture to fit it into different unused spaces, but you could get up to 8x28 by doing so.

(The red, green, and blue pixels would line up with each other to make a square in the editor/ingame)
(Potentially, by mixing ideas together, you could make the ears an 8x12 area to get the area of the tail up to 8x36, and have the editor take a separate 8x36 tail texture and automatically place it into the 64x64 output, but that might be a bit too much hassle)