True, but not every event results in a device status change. Furthermore, a UI (or anything else) querying the cloud for device status could just as easily result in a back-end real-time query to the hub for status information. It doesn’t all have to come from the cloud database.
I really hope IFTTT isn’t polling SmartThings - I really hope they are using a publish/subscribe or push model. In any event (no pun intended), an internal (platform) IFTTT SmartApp in the cloud could subscribe to the needed events for IFTTT and efficiently cache or push them to IFTTT. Thus local culling can still occur, with the same event culling / subscription mechansim then used to propagate only those events needed up to the cloud, etc.
This is just an extension of the dependency graph. From a hub’s perspective, a Device Handler or SmartApp running on a different hub is akin to one running in the cloud. (Assuming we don’t want to add the complication of direct hub-to-hub connectivity. Adding this complexity is probably best left to later, after stabilising the new architecture and after we’ve gathered enough data to determine whether it’s worth pursuing).