Two points here.

First, automation is a new orthogonal dimension. You can have automation with or without plain text.

Second, your emphasis on "automation" leads me to believe that perhaps you misunderstand what accounting is. Accounting is not just taking a list of transactions and recording them (database, file etc). That is called bookkeeping. Yes, accounting is also amenable to automation, but much less so than bookkeeping. Although, you could argue that when applied to the life of a normal individual, accounting and bookkeeping are almost indistinguishable. You have income, you have costs, and you have a mortgage - pretty straightforward. My point is in general you cannot entirely automate accounting. The reason for that is that accounting isn't just processing bytes, but instead requires the understanding of the underlying economics associated with the transactions. This understanding in turn isn't stored anywhere other than the accountant's mental model of the entity he's doing the accounting for.

EDIT: Just to be clear, I don't disagree with you that accounting could use more automation. Everything could use more automation. But for something it's more straightforward than others.

I think many accountants would laugh at saying accuracy is a requirement. They have full time jobs because the books for any major company are a disaster that are kept together by prayer and duct tape. Accuracy is the ideal, but when you have hundreds of revenue streams, discounts, rebates, deprecation, tax structures, salesmen actively trying to sell out the company, etc keeping the books in order is a tall order.

I suppose one problem with this is that accounting needs legal responsibility in case of mistakes. Software usually (if not always) does not guarantee anything (in the legal sense) and its seller/producer does not assume any responsibility whatsoever.

This! It blows my mind every bank doesn't have a sort of scripting language of some sort that let's me automate whatever I want to happen. I've seen a few services that supposedly enable this but their prone to breakage, don't support one bank or another, or are simply way too expensive.

100% on the UI. My main gripe with GnuCash is that it's impossible to do "mass actions" from the UI.

On the point of "library" - you know that "GnuCash the app" comes with its lib, and there's python wrappers? I've only ever used these to produce reports (read, reports different from the ones provided by the UI). However I believe it's also possible to do things like inserting transactions via these python wrappers.

Another example of something which is possible via the python wrappers is labels. GnuCash doesn't support labels, but it supports adding general text to each transaction and to each leg of each transaction. So you can e.g. use hashtags in the text, and then consume transactions into python and aggregate on these hashtags, making them effectively labels.