Is Superset mature enough? We have been exploring a lot of BI tools so much so that we near scraping the bottom of the barrel. But Caravel/Superset never came up because it is still under incubation and that doesn't go well with the enterprise managers. It doesn't help that there have been constant name changes.
I think there are just certain scenarios it may not support, like at one point writing queries in the editor for JSONB fields in Postgres was either hard or impossible, things like that. But generally it's pretty great and ready to be used IMO.