The first iOS Fedi app that incorporates hashtag lists to browse multiple hashtags in the same feed along with a way to save frequently used hashtags to the composer with CamelCase support (I call it a Hashtag Drawer for lack of better terms) will be the most awesome Fedi app ever!
IceCubes remembers frequently used hashtags, but only if you use the specific hashtag button in the UI, not the keyboard, and it doesn't remember CamelCase.
Ivory remembers CamelCase, but AFAIK, only for tags that are in the Featured tags list on your profile and I don't know if there's a limit to how many featured hashtags could be saved there.
I mentioned those specifically because they both have browsable hashtag lists already.