You must clarify that. You are on a technical forum and that simply is not acceptable. "Mainline" is 4.16-rc2, there is only one mainline, so you are saying it's shipping with an rc quality kernel that is still in active development?
Or do you mean it comes with an LTS? "Yocto and Debian". Debian does not use mainline kernel, in fact, no linux distro does, ever. What version of debian?
There is so much work done by the great linux-sunxi community, you can see the mainlining progress for H5 processor here: http://linux-sunxi.org/Linux_mainlining_effort
Sorry, it is the middle of the night here and I am not ready to confirm on the exact Debian version, but I believe that it has not been decided yet. You can contact us directly and we will get back to you with more info on this.
I think I will give some backstory which might be relevant. This product was born out of a need to migrate from Intel Edison in our high precision GPS equipment. We looked long and hard for Edison alternatives but there were none. They were either too big, or too expensive or did not have enough computing power. So we decided to build our own.
Disclosure: I am co-founder of Emlid, the company behind Neutis. Happy to answer any questions.