I've been studying some alternate firmware, called "Papyrix", for the Xteink x3/x4 ereader. This has a neat technique for achieving high quality text rendering on low-powered hardware!

It leans heavily upon the same SD card in which you store your ebooks, using custom file formats to ease locating the data it wants to transfer to the low-powered screen.

I'm keen to do the same in my merephone project, even reusing much of that code!