I said it before, and I say it again: some databases should be available for cross-wiki JOIN everywhere. This would at least include commons_p and centralauth_p but perhaps also enwiki_p and meta_p
I know that we discussed it before and better long-term solutions can be imagined (such as a data lake, etc.) but we need a solution now.
Sorry for coming at it a bit passionately. It just feels like we are choosing a path of pain for end users (let their tools break, then let us offer alternatives that they could adopt) over a path of effort for the Clouds team (let them create robust solutions for the end users and give them ample time to transition to the new method before turning off cross-wiki joins).