In two blog posts, Valve annouced New Bloom 2015 and the cancelation of Frostivus 2014. The blog posts included the reason for the cancelation of Frostivus and details about an item creation contest for New Bloom 2015. Also in the blog posts are hints of work being done to port Dota2 to the Source2 engine.
Frostivus 2014:
Having learnt their lesson from last year's Diretide drama, Valve released a blog post regarding the cancelation of Frostivus. Their reason for the cancelation of Frostivus were based around the incoming change of the current Dota2 engine; the new engine will probably be the Source2 engine. Due the work being done on the Dota2 engine, Valve felt that the high amounts of time and effort that would be spent on creating a new Frotivus game mode would be better spent on porting Dota2 to the new engine. The is because they will be making a game mode that will not only become obsolete after Frostivus but also not be compatible with the new engine. The same reason was given regarding the cancelation of Diretide.
New Bloom 2015:
Although both Frostivus and Diretide has been canceled, the New Bloom event was not. The announcement was made on the New Bloom 2015 blog post. All that was revealed in the blog post was that the event will feature new items created by the community. The new items will be selected via a contest for item creators to create items based off the themes of Chinese New Year, Chinese history and spring time. Also in the post, there is another contest for the creation of New Bloom themed merchandise hosted by a third party.
Source: Dota2.com