I have a 2012 cms4 with 65k miles. Under acceleration, there is a terrible rotational thumping feel in the steering wheel. This happens at highway speeds starting around 60+ mph. While trying to diagnose this, a slight turn to the right makes the feel worse, and left is definitely better. I would think this is either a front axle or a wheel bearing, leaning towards axle at this point. Any insight would be greatly appreciated.

 

I'd say wheel bearing. It starts softly and gets worse and worse. axles usually wear at the CV joint which causes a click it's clack noise doing slow tight turns. You can check the cv joint by feeling around the rubber boot and looking for tears or grease leaks. This could also be uneven tire wear or a badly balanced tire. Could be lots of stuff.

I'd just take it to a mechanic for an inspection. They will probably look at it for free with the hope of getting the repair job. They will just need a short drive and to put it on a lift to tell pretty easily.

 

Had the same exact issue even down to turning right making it worse. If you had the window down you could also hear a slight metallic clicking. It ended up being the drivers side wheel bearing.

 

It could also be a bad tire.

 

I'm leaning toward tread separation in a tire.
Try rotating tires (front to rear) on side at a time and see what that does first.