I can't say, but IM is going to undergo some significant changes based on
Bug 45932 – Remove IM server
In short, the IM interface in Zimbra Web Client will be retained, but the IM server backend is going to be unbundled.
This could be a good thing from your perspective, as your hosting company will be more directly responsible for selecting, configuring, and supporting the IM server, and Zimbra may be able to finalize the IM client.