see e.g. the selector at https://tools.wmflabs.org/tsreports/ . This would allow people to easily run a query on a different wiki (without needing to edit the SQL).
I think this is different than running it on multiple wikis, and probably easier to tackle...
Change 266925 had a related patch set uploaded (by Alex Monk):
[WIP] Database selection
Change 266925 merged by Yuvipanda:
Change 286094 had a related patch set uploaded (by Alex Monk):
[WIP] Revert "Revert "Database selection""