> If your medium is a mobile device, then you don't have that much "side" to put the notes in, so you have to get creative another way (you also don't have the same "hover" semantics as on desktop).

When I designed my site (https://two-wrongs.com) I figured you don't have to get creative at all. A person reading on a small screen will likely want a more condensed text, with less of the semi-relevant asides.