It might be a stretch, but I’d love to have a complete list of JSON structures for all endpoints, to use as a reference.
Some things like the WoW Item API can have a lot of possible fields (e.g. armor and weapons have a very different structure, not counting random modifiers or azerite traits), so it’s pretty much impossible to know without a lot of trial and error.
A complete model map should definetly be a part of the API documentation!
Should be totally doable to auto generate 
I do think it would be a good idea to implement, the time it took me to do it for my app was insane… Literally had to query multiple characters with different kind of items to make sure I was covering every possible JSON structure and I’m not sure I even have everything…
I did that for wow, d3 and sc2… It would’ve been so much easier with a JSON structure.
Supply an OpenAPI (OAS3) document or something.
It would make it easy to auto-generate a client for your language of choice.
I agree. It would be really nice to know the complete structure of all responses, specially for Go / Other compiled language users.
I have to fetch all data (cache) from all endpoints before actually parsing them into my relational database in wow-query because of those optional fields. Having an official schema would be awesome.
Meanwhile I shared some empty json files I use on wow-query for anyone interested. It is not complete, just the most important endpoints.
I generate them by merging all JSON responses from each of those endpoints so they should be complete since I download the whole data.