Aileen makes a good point.
But seriously though, I'm confused about what just happened. I think there are two interesting ideas being proposed here.
One the examination of a theoretical argument -- that English Wikipedia is a type of system that requires adaptive capacity in order to survive and that a decline in its adaptive capacity has caused measurable declines in fitness metrics. This came paired with a call to action -- to ask "why not?"
The other is an insightful feature request to include results from related wikis when using Special:Search. Given the availability of the search API[1], the worst technical hurdles seem to have been circumvented. If a reasonable justification can be given[2], the search team might pick it up. Patch sets, of course, would be fastest.
-Aaron