This is really neat. It's similar to the BuJo rapid-logging-inspired system I handspun for myself around Markdown a few years ago that I outlined here:

https://news.ycombinator.com/item?id=21580133

I'd quit using that one since because too many Markdown editors have forgotten tabs are legal whitespace after a UL bullet, and that there are three different UL bullet characters (and it really doesn't help that the CommonMark examples page only docs `-` and `*`, even though `+` is part of the CommonMark spec too). In particular, without the tab support being implemented, there's no fixed gutter for the BuJo-style sigil and queries get much harder.

But I do miss the idea of those simple bullets. I may have to check out your extension.

When I saw the OP's format, I immediately wanted a VS Code extension for it. This looks great, installing it as we speak.

In fact, I like your format slightly more, because when I complete tasks I usually just delete them -- no need for a checkbox.