Why? Currently I know our wiki works fine with greebo. I had some work to get a clone-wiki working sufficiently with hogfather; but still I am not sure whether I considered everything :-) Now, in order to keep hogfather-wiki also up to date I need to clone/copy the data periodically, because there will be a time when I switch over.
If I just could keep the greebo-wiki as it is and just access the source data with my test-hogfather, this could be a very smooth and elegant switch over.
In principle I think this should be an idea which could work. Every wiki-installation only takes the common source data and creates its necessary index, cache, meta, etc. data for itself.
Another idea could be, that only the wiki-source-data is stored somewhere on a server and that the wiki-engines all are at user side. Currently no idea whether such a scenario could be advantageous somehow :-)