Sigma adding to the prime lineup
With the success and quality of the Sigma 50 f/1.4 and 85 f/1.4, I'm told they'll be adding more fast primes to the lineup over the next 18 months.
Lenses on the horizon may include a 24 f/1.4, 35 f/1.4 and 135 f/2.
Sigma will also continue to update lenses by adding OS to them. The 300 f/2.8 may be the first to get OS along with the 500 f/4.5. With the pricing of the new Canon lenses in these focal ranges, I wouldn't be shocked to see Sigma do something 20% cheaper.