Collaboration between PWB and AWB would probably be useful in general. I believe they are the two most complete bot frameworks, but feel free to add other Phab projects for MW clients which have similar sized cross language/project userbases.
There is very likely to be features that can be 'shared' between Pywikibot and AutoWikiBrowser, despite being different frameworks and programming languages.
Design work can be re-used. Regex's and test cases can be compared to ensure they handle all the same corner cases.
We could even have PWB on IronPython running as an AWB plugin. More crazy ideas anyone?