The things on the end could be stabilizers of some sort for slipstream or transwarp travel.
I see those coils as helping to smoothen the transition from slipstream, warp, transwarp, and/or normal space, or to make sure the slipstream window and/or transwarp conduit closes without causing any damage/disturbance to normal space, or vice versa.
WTF? Are you spying on me? I had just now decided that that is exactly what they're for!
When those rings are spinning, I'd imagine they make quite a fuss as they whip and churn and in that manner fold space into a frothy lather to achieve their warp effect.
What? You think you're the only resident Chief Engineer?
At least glancing through starship design schematics is a requirement for any starship designer, even if I'm constantly employing technology to occasionally circumvent occasional technical limitations. Every starship designer knows that the best place to put any space-resmoothing apparatuses is at the rear tip of the ship.
Though maybe it was one of your assistant engineers who mentioned something, and I just put two-and-two together!