So I totally understand that it’s easier for Mondo to maintain default categories (then they can make meaningful analysis and suggestions), but I also think that default categories are crucial. So the key is to find a solution to it, which wouldn’t be too heavy on the tech side.
I suggest an option to rename current categories (retaining the meaning but customising to your needs, e.g. I’d change ‘Eating out’ to ‘Going out’, because I eat out daily at work, but I wouldn’t consider these expenses different from buying groceries, whereas ‘Going out’ is quite different) and having a limited number of custom categories. Then it would allow for some level of customisation, but wouldn’t be too difficult to implement technically and to use in analysis and reporting.
Or – having major default categories for default reporting, and custom hashtags (as you had in the beginning, I suppose, at least it’s shown in the video) for export into CSV (and then users can do whatever they want with it).
Splitting and such is useful but non-essential. In the end, it’s a banking account, not a budgeting app. Maybe if you implement ‘split the bill’ function (allowing to split the bill with friends), you could also integrate categories into that.