Techies was a massive surprise last year, but wait to see what Valve is preparing. Valve revealed the new 24-multiplayer mode in Dota 2, and also a new hero coming out soon. Reddit says that this hero must have been revealed already, but Valve prefers to take its time.
It seems like Pit Lord and Arc Warden, two of the major heroes from the first DotA will appear before the International 6 in 2016. Erik Johnson from VALVE said that both of them are expected until the TI6. It is also unclear which one of them will come out first. Since the International 4, VALVE released three heroes, Winter Wyvern, Oracle and Techies.