The Tamron 35-150mm f/2-2.8 Di III VXD has a very fast and interesting variable apeture design that we will hopefully see more of in the future. From 35mm up to 40mm the lens is an f/2, but when you reach 40-60mm it is f/2.2 and by 60-80mm f/2.5 and finally 80-150mm f/2.8. I think most would have been happy with a consistent f/2.8 throughout the zoom range, but f/2 is always appreciated.
Back in the day, there were some f/2 constant zooms from companies like Olympus and it would be great to see f/2 zooms return as the norm since f/2.8 is a bit slow for me. I generally shoot glass that is around f/1.4 as often as I can, which is why I have far more prime lenses than zoom lenses for all of my camera bodies, but I would love to pick up some f/2 zoom lenses.
Tamron 35-150mm f/2-2.8 Di III VXD (Coming Soon):
B&H Photo / Amazon
Tamron 28-75mm f/2.8 Di III RXD G2 (Coming Soon):
B&H Photo / Amazon