I don't think this approach applies to Onda, because it is not a ported device in the sense of Hammerhead. It's a device that is closest to the Jolla Tablet, which has multiple implications. The main implication being all the proprietary stuff, which you will never be able to get on Hammerhead, works there out of the box (and that makes it very unique). The other implication is that you can't really build it from scratch, because you don't have sources to the proprietary stuff and you would instantly kill the uniqueness of Onda V820w if you tried to build it without them. It is however worrying that there are differences between Jolla Tablet and Onda V820w that prevent smooth upgrade process.