[delinka]

If your custom plugin distributes its output, no. Generally speaking, the output of a GPL'd program is not also subject to the GPL (quines notwithstanding.)

[ceejayoz]

WordPress's JS (and I'd argue its CSS/HTML) is much more integral part of the code for the system than mere "output", IMO.

[delinka]

Indeed. I was hoping to elicit some clarification and left out some of my own: if JS, CSS & HTML are part of the GPL'd product, I'd agree that those parts qualify as being 'distributed' to users.