The next Diablo patch is a pretty big one, but perhaps the most interesting feature is Kanai's Cube. It's a spiritual successor to the Horadric Cube present in previous games and has a number of obscenely powerful effects, as is tradition. All these have been detailed in a recent post by Blizzard, along with a video you can see below.
The cube's ability to extract and then equip legendary effects really can't be understated. It's a huge game-changer when it comes to the power level of characters in the world and the possibilities for builds. It also removes some of that feel-bad of picking up a batch of legendaries you have no use for beyond turning into magic dust.
On that same theme is the ability to re-roll them, so that once you have the legendary you're after, a little investment means you can turn it into at least a semblance of the right stats for you. Less need for the right RNG at the right time, more hitting people with big swords. There's still the element of randomness and unpredictability, of course, it's just more in the player's hands.
It being a tribute is cool. Blizzard are pretty good for this sort of thing, WoW having more than a couple of memorials to fallen heroes, both from the company and outside it. A lot of sweat and time goes into games, particularly the good ones, and I approve of any way in which those memories and that effort can be respected and remembered.
Looking forward, there's some big time rumours that Blizzard have a big reveal ready for Gamescom. Evidence points towards a World of Warcraft expansion, while logic and timing would suggest a Diablo expansion. With the patch just around the corner it would be an odd time to announce it, but Blizzard would be torn to pieces by the already-disgruntled community if a WoW expansion was announced outside Blizzcon and so soon after the last's launch.
Personally I expect it's more likely to be a Hearthstone-style small announcement (remember that HS did not start as the juggernaut it is today), a WoW-related mini-product or surprise patch rather than a full expansion. We'll see on August 5th, when Blizzard's Gamescom press conference is scheduled. No word on if it's streamed yet.