I wonder if we're watching something comparable to the birth of Linux. I'm not insinuating that Linux would go away or die or anything -- that's absurd -- but I just mean perhaps over time SerenityOS will become more and more used as a "real" OS. For what purpose(s)? No idea. But the whole project really seems to have staying power.
That said, I'm fully with Andreas that having fun and simply building something because you want it to exist are valid goals in and of themselves. Couldn't be happier for him and everyone who contributes to the project.