To start, I think refinements to the current pro features, as they’re mostly pretty basic.
Custom categories should allow you to choose an icon (matching the style of the standard set of categories). This would make them feel a bit more equal to the standard categories.
Dummy accounts could allow adding (or subtracting) an amount as a transaction, rather than re-entering the balance. Then at least you could see what has been paid in there (albeit entered manually).
Exporting could allow choosing date ranges, or filtering what to export by account etc.
Renaming transactions would be better if it could detect certain names and automatically rename them.
They just all feel a little basic. Whilst I’m suggesting things, please add an export/share option for attached screenshots, so I can export my receipt images for my expenses. Currently screenshotting them, which isn’t as elegant.