hi @jreidinger yest that change works and it seems clearer. Thought, came to mi mind last night, there is a 
reason why i added that class, and it is that i wanted to add a multi-plugin loader in the first implementation (as 
just mention in ExternalWidgets class), and gave up earlier 'cause my little spare time. If we leave base Factory to be declared by user into her/his extension, we can have just one and only one Factory and so one extension plugin only.
I'm open to discuss, if we want to leave this open or not, a later change is possible of course, but will break any API in plugin implementation.
Let me know your (and if possible , also @mvidner) decision asap.
Thanks
Angelo (p.s. i asked for pull request also for yui-gtk for a fixing of crash I experienced)