You’re looking at 3 features in 1 here -
for the comments of Mondo’s Head of Design on categories, take a look at this post
https://community.monzo.com/t/custom-categories-multi-category-transactions/649/14?u=alexs
for Hugo’s comments on splitting single transactions into multiple categories, see this post
https://community.monzo.com/t/custom-categories-multi-category-transactions/649/14?u=alexs
& for the discussion about converting the receipt’s text (using Optical Character Recognition) and capturing it in the app, there’s this post
These are popular requests and my guess is that these features will get more attention after the launch of goals / targets, which will hopefully be any day now…
There might even be some changes to categories when that next update is released.