From what I have read, I have come to understand that all WordPress plugins,(including premium ones) should be GPL licensed. If this is the case, can the installation be limited to a single domain? As far as I understand, GPL allows you to reuse the code. Doesn't it? I'm asking this because I have seen some premium plugins have single site/multi site licenses. Please correct me if this question is wrong.
GPL prohibits restricting the code in any way. You can restrict the support or non GPL parts of the plugin (images/css) to a single domain but you can't restrict the GPL code to a single domain.
MATT MULLENWEG's response to the same question: