There are other people who have had even larger homes, it just depends on the details. See the following two threads:
FAQ: Create an all-around z-wave presence in a 4,000 sq ft home?
My concern is more whether smartThings itself is a reliable enough platform For what your uncle will expect. And I would say the answer typically is no at the current time. The more devices, the more points of vulnerability. And as smartthings staff have said many times, their typical customer has 15 or fewer devices and never uses any custom code. People keep running into various limits just in the app itself as far as how many items it will display, how many rooms it will allow for, etc. which show they aren’t really designing for very large systems.
It would help a lot if we knew what country the home is in. That does affect device availability.
I would probably consider zigbee rather than Z wave for a very large home, but that’s just my own preference. 