I'm assuming the Kindle is using an i.MX6 or better NXP SOC, because they are basically the only ones shipping an integrated EPD controller with Linux drivers,

I'm assuming the Kindle is using an i.MX6 or better NXP SOC, because they are basically the only ones shipping an integrated EPD controller with Linux drivers, which should be more than capable of parsing and rendering HTML. The Remarkable series runs Qt on these chips and is able to render ePub documents just fine.