I've got a post-64 Model 94 and the finish is petty much toast. It has assumed a purple-ish coloration, at least where the finish remains.

Since this is a cast receiver and not machined and the metal seems to dislike being blued I was wondering if maybe I could have it case hardened. The other option would be Cerakote or Gunkote. Or BBQ paint...

I'm looking for opinions and suggestions.

Your best option is to contact the Doug Turnbull company and ask if they can color case the receiver.
They're the real experts on this in America, and can tell you the straight facts.
Since Winchester did sell color case hardened limited production commemorative Model 1894 rifles, this is likely something that can be done.

Turnbull are internationally known firearms restorers.

http://www.turnbullmfg.com/

However, bluing chemicals have been developed that will allow the Winchester receivers to be blued.
For info on this, contact one of the top gun refinisher services who offer bluing:

http://www.apwcogan.com/

http://www.fordsguns.com/

http://www.gunbluing.com/

http://www.elitecustomguns.com/index1.htm