FWIW, the problem with deploying SMW on Wikimedia sites like Wikipedia has always been that it's a big codebase (tens of thousands of lines), which shares few to no active developers with MediaWiki proper, and which has had never had thorough review by core MediaWiki developers for security or performance. It would need a great deal of resources to review, and it's certain that large parts would have to be rewritten or disabled to meet Wikipedia's performance requirements and MediaWiki coding standards. From the perspective of the people making decisions on this sort of thing for Wikimedia, it would probably be less effort to rewrite from scratch.
If Erik Moeller said it was "unclear" whether SMW is up to to task of running on Wikipedia, he was either being polite or didn't ask core developers who have looked at it. It's not. I don't say this to be negative -- it's an awesome project, and its functionality is absolutely make-or-break for countless small to medium MediaWiki installs. But it's not possible for a project of this scale to be usable on a site as large as Wikipedia unless it was written that way to begin with, and (like almost all software) it wasn't. Even if it were, the kind of general-purpose data-munging that makes some SMW-related extensions so valuable is just not possible to do on very large datasets.
So I can pretty confidently say that awesome though it may be, SMW is not going to be enabled on Wikipedia at any time in the foreseeable future.