You have an in-built fatal flaw:
News organizations, especially ones with just one medium-sized digital property (this applies to many independent daily newspapers, for example), have a terrible time retaining technical talent. These organizations generally don’t employ more than a few such professionals, making the risk of attrition very high— and attrition is almost always cultural. Using a common framework like WordPress at least gives the next programmer a head start on understanding what his predecessor did.
Here's another side to the same equation: if you can retain your talent, the chances are you've got mediocre programmers working on your CMS, given how in-demand developers are right now.
This is why pretty much every journalist I know, bar those working at Buzzfeed and Mail Online hate their CMSes with a passion.