Rust

Plausible? Absolutely. The questions are what and why?

For notes, it seems like most people have settled on one of three things: org-mode, markdown, or free form plain text. There are some closed source tools that use a proprietary format, but fuck them.

So then the question becomes what does the backend do? Provide a way to query notes for links, topics, and todos? Keep a versioning system? Synchonization? Something else? Answer those questions and you have a project.

For references, take a look at nb, Joplin, Logseq, org-mode, anytype.

are you asking if someone would use it? probably not. sounds like a lot of work when someone can just use obsidian with plugins to get the ui they wanted

It is difficult to imagine it without an approximate idea of the way of interaction with it.

A common exercise in programming is creating a task list... Which by the way I just searched out of curiosity and I found this as first result, and doesn't look so bad taking a first look https://github.com/dezoito/rust-todo-list

Depending on what you do, it will probably only be a few lines of rust. Most of the complexity would be in the DB setup and SQL queries. Since you'll probably use an HTTP server crate that will handle all of that for you.

So, yes, it should be possible.

Even if you don't intend to make it a UI project. You should still do a shitty UI. Otherwise you will spend more time testing it than actually developing it.