That would have been a good space for experimentation if the Wikipedia monoculture hadn't stopped it from happening. One idea is you could mark specific articles or categories as forked, so that your changes in those wouldn't get pushed upstream. Overall it might be something like the Linux kernel, where there are tons of forks out there for particular device families or whatever.
As a Wikipedia example, look up Joy Milne (the lady who can smell Parkinson's disease) with a web search, then look her up on Wikipedia. Wikipedia says nothing or almost nothing. That's not an oversight, that's Wikipedia bureaucracy in action. You might be able to get an edit through by battling the bureaucracy for long enough, but if you have an interest in this illness and wanted to gather and share info about it, it would be simpler to just fork the Parkinson's article. Et cetera.
As a Wikipedia example, look up Joy Milne (the lady who can smell Parkinson's disease) with a web search, then look her up on Wikipedia. Wikipedia says nothing or almost nothing. That's not an oversight, that's Wikipedia bureaucracy in action. You might be able to get an edit through by battling the bureaucracy for long enough, but if you have an interest in this illness and wanted to gather and share info about it, it would be simpler to just fork the Parkinson's article. Et cetera.