What problems are there with enforcing GPL amongst Joomla?
* There's more licences in the open source bazaar than just GPL.
* Some of those licences are currently used by Joomla and the entire third party community to develop functionality that isn't inside the Core. Google's Summer of Code is part of this third party development pool.
* Some of these licences do not sit well with a GPL-only position statement, such as the W3C Patent Policy[1] and the MIT licence[2], the latter primarily because of commercialisation of MIT material inside Joomla!. As OSM has recieved direction from the FSF and SFLC that non-GPL work is not welcome, this harms the overall development of the Joomla! product by enforcing GPL-friendly functionality alone.
[1]
www.gnu.org/philosophy/w3c-patent.html
[2]
www.fsf.org/licensing/licenses/index_htm...IncompatibleLicenses
When the gentleman's agreement was in place, as it is currently with Mambo, nobody was harmed. Now anyone licencing a work that isn't GPL-friendly whilst working on functionality for Joomla! will be harmed with this new policy direction.
This limitation on GPL licencing limits free, open source, open standards development as much it may hurt the current commercial developers amongst Joomla! as there is no way to predict what new functionality has a GPL-friendly licence. Considering cellular media is one of the growing areas for the web, having Joomla! not talk to Nokia cellular media licenced under the Nokia Open Source License limits the adoption as to where Joomla! can grow.