The process of making bg being able to be downloaded from steam has begun. With the death of won and the latest steam update, there is new functionality in steam.
Browse games has a list of the top few 3rd party mods ( ranked by players on steam I assume ). BG is on that list. While downloading directly from that menu isn't possible at the moment, it is the first step on the path to downloading from steam and auto-updating.
Naturally we are very excited here. With won going down a few days ago and now this, an influx of new players is upon us. I am urging all players to be considerate to new players. Show them the ropes, be considerate - they haven't been playing as long as you and most of all don't be jerks.
Hopefully we can get 1.2.2 off to valve and auto-updating will follow.