I already made the mistake of buying all five seasons of 24 on DVD without realizing that it will be released on Blu-ray in the spring (it says so on the consolidated blu-ray release thread here) and I don't want to make the same mistake with Alias.

I'm not sure if will come soon. Since its already off the air, it might not be a high priority for Buena Vista to release it on Blu Ray right away. 24 makes more sense because the series is still out there so its easy to "tie in" with the marketing of the show itself to get people to buy the older series of the same show.

The rights appear to be held by a BD-supprorting (+ exclusive) studio so if you are basing on the future availability of Alias then BD is the way to go, but it doesn't seem like the series will be appearing in the near future, maybe in a year or two? Just a guess.

A year or two sounds right to me. Unless BD flops I don't see why it won't come out