I ask after reading your vacation write-up. Seems like the input side could have been a lot easier if you had a speech or text NLP interface to ledger. "$10 entertainment expense paid from MasterCard today," for example. That could be the holy grail for people who are not inclined to keep a detailed ledger, or for situations where input is difficult. (Theoretically you could email/iMessage/SMS/slack that string and have it picked up by your ledger file.)
$ ledger xact 11/5 mcd dinner 10.55
Separately, I saw you have also worked on a similar system for food logging. That got me thinking...what else could you track with a plain text file in this format? Fitness/workout info came to mind, as well as rewards points, sleep tracking, any others? Would be cool to have a single system to track all these things, which could be linked up to APIs like Fitbit, myfitnesspal, etc.
Convenience trumps plain text in this case because, unlike with finance, there's no bank statement to refer back to if you fall off the data entry wagon for a day or two. That data is instead just completely gone.