You can set the time to download the software. I always do 5 minutes after I get home. I would like to be able to set/initiate the download from my smartphone app. My Tesla is often snuggled in it's garage and ready for downloads while I'm not home.
Tesla deliberately rolls out software updates in this way because, if there's a problem with the update, it will affect relatively few cars before it is reported. Suppose the update bricks 10% of the cars, for example. Roll it out to 100 cars first, and only 10 are affected. Roll it out to the tens of thousands of Teslas already on the road, and it's a major PR disaster.
However, rather than pushing out the updates more or less randomly, it would be nice if people could sign up for early tester status. They would get the updates first, while people who rely on their car on a daily basis might choose to wait a bit for any bugs to show up and get rectified. The way it is now, the latter may get the early update including possible bugs while the former are left waiting.
I don't understand how this suggestion is significantly better than what already happens. I think you are saying you want the update right away rather than waiting for the stepwise rollout that Tesla normally does? Since the pace of rollout is a conscious decision by Tesla, I think the idea that they will abandon that approach and make everyone able to download on day 1 is very unlikely.
I like the concept. However, having so many users who are impatient like me hit their servers all at once would most likely kill them. Failed, incomplete or corrupted downloads could be a huge problem.