The thing I appreciate with Soundwave and Blackarachnia is that these are villains whose appearances will clearly contribute to the ongoing development of the series. The Dinobots and Soundwave's appearances are significant in terms of demonstrating Megatron's continual efforts to rebuild himself. Yeah okay, it's really an excuse to advertise the toys, but I think it's been written well as they're all working toward the plot conclusion of Megatron's new body.

Each of these characters have the potential to return if the writers wanted to - particularly Blackarachnia. Soundwave is a possibility since they did show a part of Soundwave that remained (and looked like his G1 alt mode!) - and the red glow suggesting that that component is sentient (so it is arguably his core processor or something).

I would like to see the Dinobots evolve into proper Autobots - and not retardabots like in the G1 cartoon (especially post season 2) but more like how they were portrayed in the G1 comics; as berserkers - and very much in the classical sense of a berserker from Norse mythology, or Beorn from The Hobbit. Like Beorn, the Dinobots are quick to anger and insanely powerful/nigh-unstoppable in battle, but they are also very kind and caring to their allies and not complete imbeciles either (Beorn is reasonably intelligent, as are the G1 comic Dinobots, especially Grimlock).

And I'd like to see them evolve through some means other than Sari's key. That's getting old. Perhaps the Dinobots could've evolved on their own, just as Soundwave did (Megatron never designed or intended for him to became self-aware - he was only meant to be a remote slave-drone and future body for Megatron).