File format considerations

When writing

I just want to read what I have written.
And write what I have not.
In other words I only want to deal with the contents.

I don’t want to get distracted by … features
Such as markup.
Or alignment.
Or shapes.
Or decoration.

My files should be backed up easily. To “the cloud” ¹. Or to other computers.

I want to edit on my computer.
Not in “the cloud”.

I should still be able to work on my files

When my editor software ² stops working.
When my computer stops working.
When my operating system vendor decides to go bankrupt. ³
When I decide I want to work on a different operating system.
Now and in the future.

As for what I have written

Software in 2035 should be able to open it correctly.
It should be readable and editable in multiple programs.
It should be convertable into modern formats (HTML for the web)
I want to see changes I make to lines I wrote easily
Searching should work well across multiple documents

In short

Proprietary formats are out of the question
“Document” formats (docx, odt, …) just complicate things

Plain text

There is only one right option: Plain text.
With Markdown ⁴ to add some fringe.