GPL question regarding modules

[philiplowman]

I looked on the GPL FAQ on the GNU site and couldn't find the answer to
this question.  There were some questions that seemed to address it but
I wasn't sure if my reasoning was correct here.

Suppose that you wrote a module to (dynamically) plug into an engine
that was licensed under the GPL.  You hold exclusive copyrights to the
module (having written it yourself) and license it under the GPL.  You
release the module publicly.  Then one day you decide that this engine
you are plugging into really isn't buying you anything because it's the
module that you wrote that does most of the code.  You decide to
rewrite the engine that your module plugs into changing your code to
link against your new engine.  Once you have done this and are no
longer linking against GPL'd code is there anything legally stopping
you from changing the license on your module to be proprietary software
(provided that the entire module is copyrighted to you, with no
contributions from other people)?  Obviously, the original code
submitted for your module under the GPL would still be there for anyone
to use on that license, but your code that you have the copyright to
you can change to be under a proprietary license?