This’ll be a Chinese New Year themed event, and Valve want Workshop submissions based around Chinese New Year, Chinese history, and springtime. If you can do that sort of thing, upload your submissions to the Workshop with the tag “Spring2014”. If you can’t do that sort of thing, check out the Workshop submissions and vote. All submissions have to be in the Workshop by 15 January, so you don’t have too long.
As for Year of the Horse… well, I don’t know. Arc Warden’s original Dota model had a dog head, so if this event will see another hero release, he could theoretically have been changed to be more equine. As far as I know, though, there’s nothing to do with him in the Dota 2 files, and the most recent update to the unreleased heroes had Phoenix’s alpha textures added to the game files. I suspect we’ll have to wait and see, and I suspect that the horse picture above might not be related to a hero. Oh well.