I recently came across this interesting low cost e-paper which features a backlight:
epaper display E paper display GDE0213B1 with matched front light used for dark place
It does seem that backlight might be useful as the Open Hardware Summit will be indoors.
I may order one of these displays to see how difficult it is to interface. The advantage of Waveshare is that there is already a working library with the ESP trINKet design.