There’s a lot of good information in this post:
http://www.pbs.org/mediashift/2015/01/why-its-risky-business-for-publishers-to-build-their-own-cms/
“Technology is strategy, and culture eats strategy for breakfast.”
“This is to say nothing of the most fatal flaw in the “roll your own CMS” plan. 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.”
There is more risk in going out on your own than working with an established CMS like WordPress.