my idea of a 'perfect' bb would be a sort of toolkit. that consists of many tiny templates for all sorts of functions.
those put together in a nice punbb forum template would build the forum.
if you make major changes, you could always say: the default template(s) is changed. only unaltered templates are supported. and the toolkit changed as well as so did the documentation of it.
this would provide users that use an out-of-the-box punbb a new template. and those that have build their own template would be able to have a look at the new toolkit. decide which new tiny templates they want to use and where to put them.
was that clear in a way?
regards
/christian