Why not YAML or JSON and the vetted libraries to read and write the format?
As a user I don’t really have any concern with what underlying data format and structure it stores things in. I want to manage my todos!
This could be an SQLITE file for all I care.
Software engineering should be about more productive UX, not flexing one’s ability to parse arbitrary syntactic art.
Tasks lists are generally useless without their context. It makes sense to have tasks along their context (be it plain-text, markdown, JS, python...) Also it's more maintainable and portable. YAML/JSON/SQlite will be a headache when the user decide to migrate to another tool. This approach only require a text editor, any text editor in any platform. You can plug in whatever you prefer for syncing and sugar.
For a very few cases I use YAML to store data that isn't parsed by any program (only by me). And I can write a comment like 'TODO: Do something.' or "FIXME: X isn't working.' On the terminal using a code searcher and a text editor I can easily find and jump on those.
I can easily search an SQLITE file from a CLI (wrote me a tool a long time ago to fuzzy find). I doubt the YAML lib for Python is going to become obsolete soon. I can instantly work with that format on any machine with a common language. There’s already Taskwarrior.
It’s electrons in a machine, hundreds of different paths to porting it around, changing it, etc.
Look, don’t get me wrong; I’m not about to pour sugar down someone’s gas tank. I’m just walking through my inner monologue debating this format someone chose to put up for open review and discussion.
But for things that shouldn't be normalized I write then as plain-text notes using markdown notation. It isn't true that nothing can parse plain text. I wrote a tool to do that and it works as expected. Of course it's bad design if you look exclusively from the software engineering perspective but ergonomics also matter and parsing text isn't hard.
Don't get me wrong also. I'm just a guy with peculiar use cases and bad experiences migrating away from Evernote and later Joplin.
Lindy Effect type thoughts, why import another dependency; familiarity, existing portability, and habits with current formats; deep and wide tooling and language support… road built; let’s drive to shovel poetic drivel out the door.