If I want human readable files I think I would opt for just a bunch of markdown files in a directory structure before I go the recutils route. If I want a lightweight database I think I would go for SQLite like others have already mentioned. In what situation do you really run into that you need human readable/editable referential integrity?
You can do this with SQLite but it would require CSV export:
The idea is to take full advantage of plain text, just like, markdown! You could even use git for versioning.
Just like markdown provides a quick way in that to renderize something pretty, but is still readable in plain text, recfiles do the same for data, it has data types, keys, integrity, and is easily queryable with its tools, and also easily read in plain text.
Sure, you could use some type CSV, but that is not pretty to read as recfiles. The point is the same as markdown, usable as just text, but with good tooling around it.
with markdown files in a dirs, you would have to provide you own tooling.
Let me be clear, I get that you don't have db operations with a bunch of markdown files with a directory structure, but on small scale data repositories do you really need that? For example, if I have a bunch of recipes in my "personal database of markdown files" I can quickly find the chili recipe I'm looking for by going to the directory "Soups & Salads > Chili > Slow Cooker Chili Recipe" or something along those lines. Or I could have grepped for "slow cooker chili". Either way I'm going to find that recipe with no extra tooling on my part.
Where do rec files features add value? Plus, if I use rec files now it seems I have to build my own formatting because I can't rely on markdown editors to build it automatically for me. Or is there a way to specify formatting for rec files?