Tamron has just released a 150-500mm f/5-6.7 lens for the Sony E-mount...
https://www.bhphotovideo.com/c/produ....html/overview
This would compete with the Sony 200-600mm f/5.6-6.3 lens. Although it is 100mm shorter on the long side, it is 50mm wider on the short side. It is about a half pound (215 G) lighter in weight (but, it is still a heavyweight) and uses a smaller filter (82mm vs 95mm). It is also slightly slower at the long side. Most importantly for many photographers is that the Tamron is six hundred U.S. Dollars less expensive...
Will I buy one,? Highly unlikely - I have the far lighter Sony 70-350mm and would rent the 200-600mm if I absolutely needed a longer glass. But, if I were in the market for the Sony 200-600mm lens, I would seriously consider this Tamron!
It is encouraging to see new products from Tamron and Sigma (as well as Samyang and others) for the Sony E-mount! Tamron also introduced a 11-20mm f/2.8 lens for Sony ASC cameras...