This is a great idea. Do you intend to do a serial/i2c controller for it? There are some reasonable open source/arduino serial libraries for graphic displays. The question is will this be a pixel addressable device, or is it have a bunch of symbols etched in the glass for higher res, but less flexible display. (like many battery symbols that have 4 bits to select which lvl of fullnes to display. Personally I would vote for Pixel addressable, rgb led pwm backlight and I2c controller with graphic library and either a 328 or enough flash for logos, sprites, and fonts.) Plz not a 168 with no external memory 
, but then you said hackable so that counts them out 
. A reasonable controller with code for moving around sprites means lot of simple games become simple to do able as well.
I have used some pre-defined displays in the past, but I really want a bit addressable canvas with sprites and or image in flash. Those I have used never had all the symbols I wanted, or where I really needed them. I know it hurts the cost, but it is way more hackable. I can always have the symbol I want with a simple tool to upload and manage the flash/font cache on the device. A few de-bounced switches and a few analog inputs addressable via i2c would make this a tempting front end to many projects. The question is does this push the cost too high?