Default Functions are important for most software, because end-users don't build software with compilers normally. Therefore software project has to build an execution file implementing suitable functions and release the file for end-users.
But, users discuss what suitable functions are, sometimes. Different user requests different function. To comply with requests, many software implements a plug-in architecture.
Also XOOPS has a plug-in architecture, but PHP programs don't need to be a pre-compiled application. PHP is an interpreter language, so programs is built at runtime. Therefore, Default Functions are decided by files that a project contains to a release package. If XOOPS has the same installer as Cygwin, nobody need to discuss what default functions are, because users can choose their default themselves.
"Manifesto" will be an important spec for that. Users who want fat CMS immediately may not agree the project's policy. However, XOOPS Cube project welcomes new contributors always but doesn't keep proactive programers enough. Therefore, a few programer should concentrate to develop a platform. Programers who belong to the project will develop many web application like XOOPS modules, but a mission of the project is "platform" development.