To those concerned about differences in orbital speeds, note that while dark matter appears to make outer stars move with a faster linear speed, their angular speed is not faster but rather about the same; excluding galactic cores, this basically makes galaxies appear to rotate like a rigid disc.
Yes, this is possible. But in real galaxies stars are wobbles over galactic plane, rotates around center on elliptical orbits, moved relative to each other and changes speed when entering the spiral arm. The galaxy itself changes it's spiral arms pattern. Modelling all of this is not possible. Also, all this occurred on time scale of millions of years, so SE needed global climate change simulation on planets, tectonics, simulation of orbital evolution, and evolution of the star.