Not wanting to revisit the discussion about the A20 but, instead, think about other processors that might perform better in the comparison table on this page: http://rhombus-tech.net/crowdsupply/
I have no idea if it's even reasonable to discuss these as possible options, so don't all jump on me at once. :-)
For example, the i.MX 6UltraLite could be interesting because it doesn't, as far as I can tell, contain a GPU:
https://www.nxp.com/iMX6UltraLite
I suppose some might think of it as the runt of the i.MX6 litter for that reason. ;-)
Some of the other processor families seem to be quite frugal with regards to power consumption, and can still support reasonable display resolutions. I'm thinking of the i.MX507, but perhaps also the i.MX512:
https://www.nxp.com/products/microcontrollers-and-processors/arm- processors/i.mx-applications-processors/i.mx50-processors/multimedia- applications-processors-low-power-optimization-integrated-electronic-paper- display-epd-arm-cortex-a8-core:i.MX507
I have an eReader that uses an i.MX507, so I'm probably a bit biased towards that processor.
https://www.nxp.com/products/microcontrollers-and-processors/arm- processors/i.mx-applications-processors/i.mx51-processors/applications- processors-high-performance-low-power-arm-cortex-a8-core:i.MX512
I realise that these also require support ICs, so perhaps that might make them unattractive.
Anyway, something to think about.
David