Another 5 cents to the story just popped....
Just got an AsRock A320 board for my friend's cheap-ass HTPC, and I got simultaneously bummed out and surprised.
Bummed out, cause the online store had an old description, which made me believe that it would work with my spare Bristol Ridge APU. Unfortunately for me - it was a new revision with the latest BIOS for 3000-series (e.g. some older APUs won't work due to missing microcode section). Surprised, cause it actually came with "Ryzen 3000 ready" logo on the box. So, you can shave off around $30-$40 on the motherboard, which will definitely nullify your excuse of not going 16GB DDR4.
Remember, it's a "Gaming PC on a budget". Some newer games can hog a lot of RAM. I remember before Arkham Knight came out, I was perfectly content with my 6GB DDR3 on Westmere workstation. But since then more and more games started to eat RAM for breakfast, so I bumped it all the way to 24GB just to be sure (got some cheap DDR3-2133's).
8GB is usable, but definitely not comfortable. And if you spend $700 on a PC, you sure as hell want it to be comfortable.