I'd suggest that the best place to look for that kind of info would be
here in the Changelogs section.
As a fellow Slacker, I'm sure you know that there is only one answer to all of the "Does anyone know if/when such-and-such will be available in Slack?" questions, and it's always the same: Nobody really knows except Patrick. It appears that he's busy on Slackware v10.0-RC1 right now, so whether that might include 64 bit support is anyone's guess.
It isn't clear whether you will be given an AMD 64 (as in getting new office equipment) or if you will be buying one yourself, but either way, I wouldn't change those plans. Whenever Slack does support AMD 64, you'll be ready. -- J.W.