Can WordPress be propritory ?

To answer the OP the terms of the GPL are contained in the GPL. If I – or anybody else – tell you what I think they mean we are expressing a personal opinion not making a statement of law. Whether a plugin is a derivative work or is identifiable section of that work not derived from the program, and can be reasonably considered independent and separate works in themselves; and in particular plugins or indeed themes which are not distributed as bundled with WP to which the GPL and derivative works undoubtedly applies; but are in fact distributed as “separate works” is a highly controversial subject and quite rightly one which is outside the scope of this forum. It is fair to say that many people have very well informed views on this subject. It is also true that many of them disagree. I like to always bear in mind that the very purpose of the GPL is to confer – indeed guarantee – freedoms to the user. The user includes, you, me, and anybody else including theme and plugin developers. I understand the GPL stops anyone licensing and / or patenting a deriviative of WP.

subtly different question – what wp is willing to allow in its repo………