I should note that I think it might still be possible to get your proposal un-invalidated - the question is whether your proposal is meant for WMF sites, or just for regular MediaWiki wikis. I'm guessing the latter. I think the WMF people are so used to thinking in terms of Wikipedia that some of them forget that MediaWiki is itself a WMF project, and that improving it on non-WMF wikis can still assist with the "sum of all knowledge" goal; they just assumed that you were talking about adding SOLR to Wikipedia. I have no inside knowledge on this, but that's my theory.