I am not going to say anything not yet said. But here I go.
Being this a gaming machine I think it has sense to go for the X7-Z8750 or AMD A4-Micro-6400t, but also the Z8550 would perform ok, being cheaper, (cheaper than the AMD?)
4 (I initially said 2, I meant 2 on each side) shoulder buttons are essential to me too.
4 GB RAM sound amazing for a machine like this.
The microSD slot up to 128GB amazing too, please add one that supports current class cards and will be amazing.
Wifi and Bluetooth, amazing too.
If this machine would accept Linux I would buy it without blinking at the suggested price of 250$, and I sincerely think you would expand your potential target market by a huge margin, much beyond just gamers, also all kind of hackers (in the sense of people who like tinkering with machines)
Does Intel restrict in some way the number of OSs of their low end SoCs like these ones mentioned? I think adding support for Linux would not be a big deal, and would attract many customers.