Automatic Updates already can be auto
Win2K SP3 added the new Automatic Updates process that ships with XP.
With this version, you can currently set it to "Automatically download the updates, and install them on the schedule that I specify", then you select which day of the week (or Every Day) and a time for this to happen.
Sure, it is not enabled by default, and maybe that is what is being thought for Longhorn. But I'm sure as heck not going to run it that way!
I am not the best fan of the whole Automatic Updates process anyway. I prefer to schedule patch maintenance times, then I download and install patches that have been out for a while. I NEVER run a patch that just came out. I have seen several patches that were recalled due to problems.
To let a system automatically download and install its own patches in the middle of the night will just lead to phone calls in the middle of the night when the server does not come back up!