That's missing the point. Full Internet access is just too broad. Going to wikipedia and aimlessly browsing about is fun, but a more educative approach can narrow the focus for students and especially for younger learners.

How to market it in developed countries is going to be a tough nut to crack though.

Well there is nothing stopping any school in the developed world from loading this on to a pi or something and having everyone use it too. It's free and open source (from what I can tell).

It's aimed at places with little to no, or unreliable, internet. So if you have normal internet speed there is nothing you can't get that's on the box. Also it seems that its not even a curated Wikipedia, it's just a full clone of it (assuming for whatever language your downloading)

Plenty of schools have network control over the devices that are used in schools, meaning that you can indeed narrow the focus by only allowing a few websites to be accessed.

My kid's school uses a software called GoGuardian, which allows individual teachers to whitelist specific websites for the students in their class during their class period.