It's been in the Liquid road map for a long time.

We're using them for Ark too. No production yet. We use the root keyspend for the cosigning (clArk) and the leaf for the expiration clause.  

 Ark when ready will be one of the first "real" usecases for taproot i think? 

 Not really. I mean it's just doing an OR. Taro will. BitVM will. MATT will. Liquid's big multisig also would be. 

 taro is taproot assets, already in use and on my list, i consider this one of the first,

everything else you mentioned is still in the works? or are you naming off things that have usage? 

 Mentioning "real" use cases. Yeah sorry, you mentioned in production. These are not.