Microsoft has indicated that they are going to be updating the Exchange Online Protection addresses in January 2015. Here is a link with the new IP addresses:
Also, it is not explicitly stated, but I would be concerned that mailflow for hybrid environments will be affected. So, it may be necessary to go into the receive connector used for hybrid mailflow and allow these IP addresses there also. I'll try to check on my hybrid system when the changes go into effect in January and update this post.