Hey,
I'd say it's well informed paranoia. SMW is used on some largish wikis at
Wikia and it apparently causes issues very often. The largest wiki with SMW at Wikia is very small in comparison to a lot of WMF wikis.
SMW has historically had a touch of the featuritis. Most of its features
would need to be disabled on WMF wikis due to performance reasons, and then what's the point?
I fully agree with you when speaking about Wikipedia or whatnot. SMW, like any software, has it's issues. Knowing these I think it'd be a bad idea to try to deploy it on Wikipedia or Commons or whatever in its current state. Wikitech and MediaWiki wikis are a different story though. The ill-informed paranoia I was referring to consists out of thinking something not far from "SMW will make any wiki uber-complicated and explode". This certainly does not include concerns with deployment on the big WMF project wikis, which should be taken seriously.
Cheers
-- Jeroen De Dauw http://www.bn2vs.com Don't panic. Don't be evil. --