> How often is numerical (which is the only knowledge you can really automate this way) knowledge updated?
Numerical knowledge is not the only knowledge that is stored there.
I'm going to go with update rate of often. It has a higher edit rate than english wikipedia does.
> How often is said knowledge dependent on cultural idiosyncracies?
Sometimes that is true, other times it isn't. The system is used where it makes sense, and not used where it doesn't.
> How much effort is the code maintenance of the specialised editing system? How much effort is maintainance of the centralised infrastructure.
There is certainly some. I wouldn't say its dominating, but it certainly exists. There is plenty of centralized infrastructure for other things too.
Prior to the introduction of wikidata, more complex fragile systems existed to try and keep things in sync in a more manual fashion. They also had a cost.
> How much effort is it really to change the data in multiple places, given that enough eyes every bug is shallow?
A lot. And we don't have that many eyes in lots of languages. There's a lot after all: https://en.wikipedia.org/wiki/Special:SiteMatrix
> What are the oppirtunity costs of not being able to properly distribute and share articles because they are suddenly tied to a very specific codebase
Not sure what this has to do with it. Articles are written in a custom markup language. That's already tying it to a specific code base quite heavily. The wikidata dependency is pretty trivial, and there are open apis to get info out of wikidata, and regularly made dumps of all the data in wikidata if you want to copy it. If that's not good enough, just copy the rendered version instead of the source.
> How much infrastructure cost do I have because I can't get volunteers to host my data
I'm not sure what you're talking about. Wikipedia was never hosted in some magical peer-to-peer fashion on volunteer web servers, nor is there any situation where it is likely to be hosted that way. The goals of (near) instant update time, as well as some central quality control and user blocking, makes distributed hosting pretty impossible.