There you have it, straight from the Frog's mouth. While nothing is set in stone for now, it is safe to say that there will be quite a few heroes being introduced in the new map version. On screenshots posted on other forums you can see a Kodo and a Phoenix. But will it be the five or six, as mentioned by IceFrog?
Gosugamers will keep you updated with the development of the latest version of DotA.
Links
Gosugamers.net - Forum discussion
Playdota - IceFrog's post