I have written to the authors of AAChoo and AACelerator in regards to any plans for a Windows port and have yet to receive a response. I would have more faith in the chance of an AAChoo port (as danchr mentioned that AACelerator was just AppleScript as opposed to C), but I definitely won't hold my breath as I see both options as highly unlikely. I realize that iTunes for Windows will come along down the line, but it would be a nice option for now.
I have been debating digging into the API myself to see what I can come up with, but I was curious as to if someone might already have a head start on this? Now that 6.3 has surfaced, supposedly with a tweaked AAC encoder, this gives me a little more motivation.
Thanks.