FOX 12 Oregon I'm pretty sure would keep their branding with FOX if they could. They do not see it as a liability. Yes, people repulsed by FOX probably don't watch just due to the name, but the local content is not skewed conservative, though they do run FOX News packages to fill time. FOX 12 gets high ratings as-is, so I think they are content with their audience.
As for the logistics of changing their branding, it would be a big change to drop FOX. Like you said they could go back to the old branding of Oregon's 12, which I like but I'm not sure if it sounds fresh and modern or old timey. I'm also not sure if any instance of using their call letters as branding would be on the table. The only time they mention them is referring to their website, KPTV.com. I think it would be too clunky in opens and whatnot along with their slogan (First. Live. Local.) and show titles. Then again, I thought it was clunky when KGW dropped NewsChannel 8 from their branding and just went with KGW News, but I got used to it, but it works for them as they have no slogan or separate show names.....just KGW News at 5, etc, etc.
The duopoly station (KPDX) currently is FOX 12 Plus, but was previously branded as PDX TV which they could go back to. Maybe use some form of that on KPTV???