Well, you *can* actually do this at this moment. Create an empty simulation, add two objects, select them both and you get a nice menu with stuff you can do with those objects, like "balance selected", "zero velocities" etc.
On the bottom of this list is the "auto system" option. If you select this option the system will fill with random moonlets and the game of accretion will begin.
I've started one of these sims yesterday. After 150 years of sim time I have a huge jupiter like central object, nearly a brown dwarf (17.7 jupiter masses) surrounded by a chaotic system of coalescing worldlets. Some of these wordlets can grow quite huge (0,3 jupiter masses or so) but they often fall prey to the central protostar.
Anyway, this type of simulation sure feels like solar system building. One of the feature requests I've posted before is the evolution of objects. The central protostellar mass looked like, well, the moon. So I gave it jupiter.dds and a nice reddish glow. And I'll toggle the 'emit light' button when it reaches 30 jupiter masses
Anyway, the auto system button is mesmerising. Use it at your own risk