I was very happy to see you’re now releasing this project under a real open-source license.
But under the GPL license, if I make modifications to the CMS itself, I have to release the changed source code under GPL as well. GPL is dodgy in this area, but technically, you could even demand that any website built using this CMS has to be released with full source code under GPL to the public.
I don’t think that’s what you want, but under GPL, you can legally demand of anyone building a solution with this CMS, that they release the source code under GPL - that’s why it’s commonly referred to as a “share-alike” license.
Under GPL, I can only evaluate this CMS - I can’t start building solutions for clients, since I would risk putting them (or me, or my employer) in legal trouble. I don’t think GPL is a suitable license for “library” type products, unless you’re going to dual-license this product, with an alternative paid license, under different terms.
If that’s not what you plan to do, perhaps you should consider relicensing under LGPL, which permits people to build closed-source solutions with your library, without these restrictions.
The bottom line is that no one is going to build commercial websites under a share-alike license - with the possible exception of sites like Wikipedia