Hi,
Can I bring up a little issue that might be problematic regarding the fact that ProcessWire is licensed under the GPL Version 2.
This has implications for things like extensions in that the GPL may require them also to be distributed under the same license. The GPL affords users rights in how they use the software and permits them to enhance and, more importantly, re-distribute those enhancements. This is fundamentally at odds with making extensions commercially licensed and I would suggest that you clarify the position with the Free Software Foundation (Bradley Kuhn is a good contact for this).
I should also mention that introducing commercial extensions to ProcessWire may tempt others to do things like obfuscate code or require the use of module loaders to protect the commercialism of their extensions. If the GPL applies to extensions through ProcessWire then this is totally at odds with that license.
The introduction of commercial extensions to ProcessWire has inadvertently changed the nature of the project. Although you describe ProcessWire as Open Source it was actually provided under a Free Software license (there is a distinction) and now that statement only applies to the ProcessWire core and not these commercially licensed extensions.
I am in no way against people making money from Free Software/Open Source but it is important to realise that, when commercialism enters into a project, sometimes the initial choice of a Free Software license is not appropriate.
Regards,
Neil Darlow