I don't see fixed baudrate as a problem. The tradeoff in variable baudrates can be erratic, unpredictable startup.
I've got a simple solution to users borking their baud rates. 
Just a a pair of contacts. Short them out with a screwdriver or similar and apply power. Resets to defaults.
No Feedback ... that would be nice, the cost is another connection and i/o line
The feature would be completely optional. I2C and SPI can have a polled mode where the host asks if its ok to send.
If your using serial and dont have a spare gpio then you just ignore it.
You are right and wrong about 'special features' there is some provision to send binary commands that could enable dot-row/column scrolling and other 'special effects.' But that indeed does pass an increased burden on the host processor.
Well I did say that the chip was 'dumb' and only did what it was told.
I dont see why you wouldnt add in special effects considering the chip is mostly idling and it cant be using too much flash space.
I'll hopefully have a beta firmware in a week or two. 
Then I can get a prototype going and calculate costs and stuff like that.