I thought big portion of need that data mesh fills is the organizations who are missing resources in their core BI team.
For bringing data in, thats completely different story, especially in non-tech organizations. The gap between how power user from specific department and somebody from my team brings and transforms data is still too big and somehow hard to enforce (following naming conventions, keeping same data formats for same columns, lowercasing certain columns, so joins are done correctly...). They usually have their "playground schemas" they use, but its very far from saying that they "own" data quality there.
IMO - To make it work you need a consistent taxonomy or way of translating from a particular domain to some sort of interchange format.
If you have that then a set of centralized tools can pull from the separate domains using a core set of protocols to produce reports etc.