While I cannot offer alot in terms of experience with the IVT, I can tell you my impressions after a couple of weeks in the saddle. The word used the most by myself and other passengers regarding the car in general is "smooth". With the drive mode in "normal", 0-50mph is an effortless exercise once you find the sweet spot in the throttle. It feels almost like an electric car once this is achieved and Hyundai did an excellent job with throttle mapping in this mode.
Is it fast?...no, but it manages the power very well. The lack of power is only relevant at speeds over 60mph when merging onto interstates, but in start/stop traffic it is a joy to drive compared to the clutch operation found in a manual. I just got rid of my DD which was a 2013 Sonic RS with a 6 speed stick. Super fun out of the city, but I do not miss the clutch in the city.
The IVT performs well so far and I feel like it will get better with more break in. Im not sure if Hyundai uses "intelligent" programming to help with downshift sequences, particularly when grading is involved, but if it does learn...it will only get better the more I drive it.
Longevity is the question for me at this point, and only time will tell. I really hope it holds up because i can honestly say it is one of the best cvt transmissions I have drove to date.
Hope this helps.