One size fits all never worked. It doesn't with underwear, it doesn't even with socks. Sorry. Cutting corners here will only mean that your OS will be the WORST choice on ALL products. Because every other product in the market that is fitted to the type of device it is meant to run on will have a better suited interface and give the user a better experience.
One size fits all is nothing but a mediocre compromise, and by definition inferior to any specialized solution.