You might want to check out ImageMap , if you just use the annotation to generate links to more specific room information, like when you have a map (uploaded as an image) and then you click on some room in the map and then you get to a different wiki page about that room like "There is a HD projector and 150 chairs...".
The map extensions you mentioned will display small images with map pieces called "tiles" made by externals in your wiki. There is something like a "Wikipedia for maps" - OpenStreetMap  and you could consider adding your data to their publically available database. This would require you to release the data under OpenDatabaseLicense publically . If you want to do that, you would probably need to transform your data format to match theirs and consult the community before importing  and finally you would need to produce the tiles from their data, because standart display do not show the indoor features. Further information is available from the relevant wiki page . This is pretty much what Wikimedia did with their custom "Kartographer" . Seems like a rather complex way for just showing a floor plan, but that is essentially the infrastructure behind "Maps" and "OpenLayers".
Is anyone doing this?
I am currently working with "MultiMaps" , which is essentially working the same way as Yaron already described but without Semantic MW. I am just displaying the standard tiles provided by OSM.
What do people here recommend?
Sorry, I can not really recommend anything for you, because it depends on the following facts
How many maps do you have? (huge maps make the OSM approach more interesting)
What do you exactly expect from "annotations"? (simple links, texts on top of the map, geometric shapes?)
Can you publish the data under ODbL? (see above)
How often do you update the maps? (no updates, continuous updates, real-time)
 https://www.mediawiki.org/wiki/Extension:ImageMap there is an example as well on that page
 https://www.openstreetmap.org (personal disclaimer: I am involved in this project)
 https://opendatacommons.org/licenses/odbl/ (comparable to CC-BY-SA as far as I can judge)