It's an interesting idea on the whole, but one thing does occur to me: there seems to be no real cause for their devolution.
I can agree that having them devolve into the Swarm than evolve from it, but there needs to be something of a catalyst behind them falling apart. It could be anything from outside influence to internal madness.

Just as a quick example, it could have been out of becoming obsolete for some reason. We saw during Beast Wars that most of their existence seemed to revolve around seeding worlds with energon. If their duty of creating energon ended then they would have no reason to exist and no purpose in the universe, thus leading into devolvution. This isn’t a perfect idea but it’s more an example for what could be done involving them.