The latest Dota 2 blog entry indicates that Valve is ready to move the game over to Source Engine 2 in the first half of 2015.
As we mentioned in September, there are a number of features in the works for Dota 2 that we’re really excited to share with you. Among them is a major improvement to Dota 2’s engine that we are aiming to release in the first half of next year. One of the main features in this engine improvement will be the ability to rapidly create entirely new game modes. You’ve seen some of this work with the Dota 2 Workshop Tools Alpha that began earlier this year. In the past, our Diretide and Frostivus updates contained game modes that were very time consuming to build and maintain, and would need to be rebuilt from the ground up after the release of the engine update.
Diretide was skipped over this year for a few reasons. Valve says that the first reason is that the mode would become obsolete when the new engine changes arrive. The second reason is that creating Diretide would take away from resources needed to work on the engine change itself. The same reasons apply to the lack of a Frostivus event for 2014.
Valve is planning the New Bloom Festival for February, but other new game modes will have to wait until after the engine update.