Watching this atm, it's a podcast but they have Jonathan from GGG explaining a lot of the changes directly on his dev client. For example he explains how the instant movement skill works out. Basically the delay is added as a hidden cooldown after the skill is used, so if you repeat the skill, it'll be delayed longer, which gives the same speed for moving around as currently live, but it gives a much faster reaction when you're using movement skills to dodge stuff.
Edit: Finished watching, was really informative. Seems they are changing a lot of core things, they changed how their distance system is calculated, which led to changing how the pathfinding is calculated, and now it's 8directions instead of 4 so it should make pathfindings in various cases like weaving into monsters or using movement skills near edges a lot more fluid. Also the animation changes they're doing makes it so the animation follow the movement of the skills kinda, so for example if a mob is swinging left to right, if you dodge right you have more time to avoid it than if you dodge backward, shit like that.
Lots of preview of changes too like bleed/poison changes(no details just that they're changing some), physical damage and melee damage will have bonus to stunning while casting and elemental will have penalties, support gems for each weapon type, 2 new movement skills for low lvl(dash for melees and an undisclosed one for casters), a low level defense skill(maybe another I'm not sure) that negates a lot of damage for a short time up to a treshold and molten shell is changed the same way but scales the treshold on armor so armor stacking with molten shell actually gives relevant mitigation against bosses. He shows how cyclone works with weapon range and that's probably the big ass cyclone shit that they've shown, if you use a 2H with the weapon range stuff, unique, tree and what not you'll get the big cyclones. Shield charge will use shield damage like Shield Throw and apparently that's being adjusted too. The new dash when used with Shift(hold still default) will instead dash backwards and he talks about how they're thinking about using that for other skills too as a modifier.