I see both HK and Khadas as different shades of the same grey when it comes to software support. HK definitely have a more active user community around their products and some reasonable staff, but you can count the number of upstream kernel/u-boot/etc. commits from those staff on the same lack of fingers as Khadas (and several other SBC vendors). At the end of the day they all have the same business model which relies on seeding free samples among the Linux community in the hope that enthusiasts will do most of the work for them. The *only* board manufacturer who gets my vote for contribution is LibreComputer; who don't code anything themselves, but have been bankrolling Amlogic GX mainline development for some time - which has directly benefitted the entire community in addition to their own products. LibreComputer customers don't need much vendor support because you can just grab the latest upstream source for kernel, u-boot, etc. and everything is already supported.
VIM3 has a reworked heatsink and fan; there are taller vanes on the heatsink and the fan (which is allegedly silent now) has swapped sides to improve the cooling .. although I wouldn't know as Khadas forgot to include one in the sample kit. I have the board in one of their fancy cases (which I think are a bit crap, but they do the job) and it's warmer than cool (and the N2) but also shows no signs of overheating and it's still nowhere near the "raging inferno" temp that mk1 AppleTV's used to reach. Once G12 devices start running at full speed I might need to check the temps - right now they're on minimum clock at 1.2GHz (and still faster than previous generations) - but then adding the fan is the obvious addition. I wouldn't want to run one for long without the heatsink.
NB: The initial VIM3 device-tree that I made was literally a 10 mins copy/paste exercise (in a Hotel room .. no special tools needed). Once we have a few more devices under our belt I think G12A/B will be an identikit exercise.