They understand pretty well the itemization that has to be put forward:
"So items have Attack, Defense, and some affix/s. Attack means damage, Defense means damage reduction. We want to simplify some of the math choices into these stats, and keep only the playstyle choices and add to the playstyle choices. What I mean is say you have a choice between 2 items, one is I deal 100 damage + 100 damage, and another says +10% damage, I don't really know which one does more damage unless I work out the math problem. But we have more damage affixes like say 'more damage against far enemies' or 'plus to talent affixes.' Plus to skill points as affixes. You can grab one of the Tier 4 talents thru items." They want to add as many playstyle affixes as possible, and make sure they're not math choices as much as they can.
Skill synergy? "Of course. especially with legendaries. Fully customize what you want to do with every single slot, and of course skill slots."
"Magic --> Rare --> Legendary. I like the idea of rares being possibly endgame items. Is this on the table?" "If many players feel like it's too much choice to decide legendary powers on every single item slot, then that could be a possibility. But where we think we want to start is they want to try giving players as much control with as many slots as possible, but if testing doesn't go well then they could try switching to that idea."
Feels like in D3 the devs dictate what the builds are going to be based on the set bonuses. That's not the direction youre taking in D4 right? "We want to create as many legendaries as possible so that people have enough options. And we want to create a scenario where we can intro new items to the game thru seasons. The most hardcore players love to discuss various things, so if there's an idea "this build would be really awesome if there was this one item.." and they can explore adding that. You'll have full customization, and we can work together with players to find what are some new types of builds you can play in future seasons."