Beyond Unicode, it should be possible to define a Web Component that generates SVG on-the-fly from a datasource.
Imagine:
<sparkline src="an image or csv"\>
One cool thing about SVG is it can inherit styles from your application, so you can produce e.g. dark-mode aware graphics rather easily, also one of the perks of this Unicode approach.
Eh, you'd probably use <rect> rather than a single <path>, because then you can trivially slice your sparkline and tag every tick with metadata. So for simple sparklines you don't really need a custom element. Page elements already follow a box model, just CSS them boxes =)
But for an annotated data set that renders as a sparkline, a custom element with an SVG shadow DOM probably makes sense. Definitely more work than the "this'll do for most folks" solution though =D
Imagine:
One cool thing about SVG is it can inherit styles from your application, so you can produce e.g. dark-mode aware graphics rather easily, also one of the perks of this Unicode approach.