Pulling the currently rendered field layout inside the CP
It looks like EntryTypeModels have a fieldLayoutId attribute. By inspecting the route params, we can get the entry type ID, and then create a model from that. Other than this, I haven't been able to find anything passed to the FLD.

    $params = craft()-&gt;urlManager-&gt;getRouteParams();
    $variables = $params['variables'];
    $matches = $variables['matches'];
    $entryTypeId = $matches['entryTypeId'];
    $entryType = EntryTypeRecord::model()-&gt;findById($entryTypeId);
    $fieldLayoutId = $entryType-&gt;fieldLayoutId;


Hopefully this helps!

Edit:

I also found that a fieldLayoutModel is passed to the fieldlayoutdesigner.html template when it is included. See the include in templates/settings/section/_entrytypes/edit.html as an example. Content from the FieldLayoutModel is then loaded. 

I know you said you would rather not load with ajax, but it is definitely better than nothing. I don't see any hook or event that gives you access to this information.

You could do something like 

var fieldLayoutId = '{{ fieldLayout.id|e('js') }}';


from within your included js file and then go pull your metadata via ajax.