Add features and Pro Version. Heres a proposition.
This app is incredibly simple. Anyone can pick it up. In fact, it's to the point where its TOO simple. Now, hear me out:
-Actual tweening with keyframes (I'll get back to that)
-A blending tool
-Layer settings (opacity, flipping, mirroring, inverting, merging, etc.)
This would be nice too, although not required:
-Blending modes (Multiply, Add, Overlay, Screen, etc.)
I'm aware that some of these features would be too advanced for a simple update.
I suggest a Pro version of Flipaclip.
Implement all the features listed (maybe ask for feedback on what the community would want), add the Premium perks to the Pro version, and charge $5-10 to keep forever. Procreate is only $10, so this would be fair competition. That way, you can have the beginner-friendly version with the minimal amount of tools, and you have something for the more professional animators out there who want to animate on mobile.
If you want references on what to add, take a look at any PC art program: Animate CC, Photoshop, Clip Studio, Medibang, Fire Alpaca; even ibisPaint X, which is both on mobile, and has many more features for FREE!