I'm absolutely in love with what you came up with here, and I definitely have to build one! I think with some careful rearranging, you might be able to fit an extra one of those LiPo cells in, and definitely could slim the body a bit further by replacing those aluminum electrolytics with tantalums or large enough ceramics. Definitely gonna try to fit these changes in if I build one.
Unfortunately it's a lot easier said than done, this thing is
crammed.
Between the battery mount and the passives/ribbon connector on the LCD is only about 3mm of space, and that was only added later when I found I didn't even have enough room to run my wires:
And on the motherboard side of things, removing the electrolytic caps and replacing them with tants would only yield about 1.5mm of savings:
And before I forget here's my pinout of the Motorola SC438001 chip used on the controller, there was no documentation anywhere online for this thing but there was for the other variants. Hopefully Google scrapes this so others are able to find it in the future:
