I'm thinking of giving markdown a try, for the reasons you say, but I'm not sure how the maths notation looks like when it's not rendered. I think it's all escaped characters, in which case it won't be as readable as plain text, even with rare glyphs that need special fonts.

Some text editors even let you enter rare characters with key combinations (frex, Vim's digraphs). The end result is pretty much WYSIWIG mathematical notation.

Here's an example from my machine learning class notes:

        ⎛ ₙ       ⎞

ƒ̂(x) = θ⎜ ∑ wᵢxᵢ ⎟

        ⎝ ⁱ⁼⁰     ⎠

So, that looks a mess on HN, but if you copy/paste it in a decent text editor, with a font that has all the necessary characters, you'll get a nice formula that you can keep around for as long as there's text editors supporting ASCII- and you don't have to rely on any special tools to render it properly.

That's what I'm going on about- but there's not enough super/subscripts in ASCII itself. :)