Taken from icefrog's blog:

"Hey guys. I'm here to give a quick update on development status. I'm still working very hard each day to try and get 6.60 to you guys as soon as possible, I know you are all waiting. While there are indeed new heroes and items in the next version, there are also lots of hero and item remakes which can be very time consuming to get right sometimes.

For Heroes, the main challenge is getting just the right mix of changes and new abilities that will both keep the existing fans of that hero happy and satisfied while also making the hero more enjoyable to other players. There are many heroes getting at least one changed ability this time around, but not every change ends up making it to the final version if they don't pass those requirements after some play testing. For Items, whenever one is added or changed, all other items need to get checked. Sometimes older items require more changes to be consistent with other game balance adjustments that are done. This is a process that items go through many times during the beta phase and it makes the exact timing of updates a bit hard to predict because the goal isn't to just change something, but to make sure it offers something enjoyable to the players in the end.

Of course there will also be lots of balance improvements as well, and not just new/remade heroes and items. However, to try and make up for the long wait, I'll share with you guys some more specific information about the next version.

Aghanim's Scepter has been remade and in addition to its new functionality, it will also provide ultimate upgrades to many other heroes that didn't get it before (and not just Intelligence heroes).

Another new feature is a dynamic terrain morphing command available on a per user basis (including trees). For example, you will be able to change to snow terrain and snow trees at any point in the game while the other players are still using the standard forest theme. The way the new system has been developed allows easy addition of more terrains without much work, so if there is a specific terrain style you like, let me know.

Thanks again for the patience, I'll do my best to give you guys an update as soon as it feels ready and when it is only a day or two away from release. My hope is that it doesn't take too much longer. I've also been receiving some pretty nice ideas through the email, so keep them coming."

There is lots of badassitude here.

Been waiting for this for over a year.