There are lots of details to be ironed out if we go the wiki way, which is why I think the tagged route would be the best start. Start getting the data and develop the larger structure over time. Once we need the data to populate the wikis/dbs/whatever, any mod can filter the posts pretty easily.
Other problems I see happening - conflicts between mods on entries, keep or throw out entries when an instance defederates (the c/politics folks might not want the entries on Biden being a lizardman from Nova Scotia, but c/iliketohitmyheadwithbricks does), bad blood if some mods want tighter control over wiki content, syncing when federating impact if larger media elements added, multiple wikis covering multiple topics while there are multiple instances covering multiple topics (multiplicative duplication due to the multiple hierarchies of equal importance), and I'm sure plenty more.