Pretty much everything is changing at smartthings, including the app and the entire backend platform. Major, major, major changes which have been affecting most of the people in this forum, hence the hundreds of replies to the two recent official posts. (The topic titles are clickable links.)
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From a hardware standpoint, changes in the last year have been firmware, but there have been some significant ones. on the Zigbee side, increasing the number of directly connected end devices from 32 to 64, support for Zigbee 3.0, and some groupcasting changes. On the Z wave side, enhanced support for the S2 security protocol. All of these are “behind-the-scenes“ changes, but still significant.
They have also rolled out official distribution and support for the V3 hub in about 17 new countries last I looked. That’s not a trivial effort, either.
As far as a V4 hub: nothing has been announced yet. I would definitely expect a 700 series model eventually, but for right now they probably have their hands full with the other changes they are working on.