For Android 7.0 upgrade -
We asked our partner to upgrade it, but I am not sure if these incapable assh*les can do it on time. MT8783V CPU that we are using can run the Android 7.1 64bit.
All the generic models with Android 7.1.2 in the market are kind of fake. it's 32bit Android 7.1.2 loosely based on Android 5.1.
Android 6.0 isn't bad for now. Since 5.1, Android got a lot of changes internally, but as far as I know, Android 6.0 is as fine as Android 7.0 on the internals.
As far as I know, Android 7.0 has certain requirements like supporting VULCAN API something like that, but MT8783V is missing something, so it cannot get 'official upgrade'.
However, I see our Taiwanese friend MediaTek has sorted it out to bypass such. The only problem is our partner who fabricates the core board would do it on time.
These assh*les are causing every misery. We might go to another partner in far future...

In conclusion, 7.1 seems possible and let's pray together for it. But 6.0 would be as fine as 7.1 for its lifetime.