I'm expecting OS X 10.7 will probably bump iChat to support Facetime, since most of the features are already there with their earlier video chat attempts. Or possibly sooner with an update delivered in iLife. Hard to say for sure though.

On Windows, not sure what they would do. They may bring iChat over similar to their work on iTunes and Quicktime, but hopefully do so in a way that doesn't make it a really bad experience. iTunes cross platform support so far has made an app that just feels bloated and sluggish on either side.