> It does add a good bit of technical complexity since there's conditional logic involved if you expand outside the Protestant canon

Indeed, and best wishes in figuring out a good approach if you go down that route! It's very understandable that tackling such complexity is not at the top of your todo list.

> I think it's low priority for the average Bible reader.

I'm not looking to debate the point, or anything like that, but wanted to suggest that "average Bible reader" might have a broader scope, depending on one's perspective.

At any given time there are millions of Catholics and Orthodox Christians around the world who are reading the Bible; consider also that there are readings (and other spoken/sung elements) in the liturgies of both East and West that originate from the deuterocanon, so it would be quite natural for someone to want to "read at home" and explore a text they heard read/sung aloud during Holy Mass or the Divine Liturgy.

In addition to the Catholic deuterocanonical books, some Orthodox denominations include many more books.

Also, another public domain translation is World English Bible.

And, if you do not have footnotes, perhaps to add it, since things can be lost in translation, or be due to the culture of the time and place, or units of measurement which are no longer common, political boundaries change, etc, you might want to know whatever notes there are of it.