Thesis’s Next Opportunity: Un-WordPress Itself

I say this as someone who a) doesn't know anything about the actual interaction between WordPress themes and the "core" WordPress code and b) doesn't fully understand the implications of the GPL in situations like the one I'm about to propose, but...

Instead of developing a clean-room WordPress clone, could someone write a sort of adapter library that abstracts away the pieces of WordPress needed by templates? That way, the templates could make calls to this hypothetical "fakewp" library, which would essentially just pass those calls along to the "real" WordPress code.

I'm assuming templates have code along the lines of:

  foreach ($WP->get_recent_posts() as $post) {
    display_post($post);
  }

that could be adapted to

  foreach ($FakePress->get_recent_posts() as $post) {
    display_post($post);
  }

(please forgive any PHP syntax problems)

Is that not feasible, for some reason? Or would the GPL mandate that this wrapper library also be released under the GPL, along with any themes using the wrapper library?