The only reason I am hesitate with E version is the lack of Grove interface and GPIOs ledout, which we deem important more application possibilities and debug scenario. And this is the most important reason that I consider a hexagonal shape, since it has enough side boundary to accommodate those connectors need to be put toward outsides. Compare to a 6565mm square, do you think a 6565mm hexagonal would be also fine to assembly?
Put the micro-SD card slot and the battery cell holder on the backside will definitely save a lot of space, but would also cause difficulty in using and assembling the board to a flat surface. What do you think?