Answering Carlos, a little spark came to me.
Do all backends support 3-union fields? Because I think I saw that MongoDB
has the tests ignored.
HBase supports them.

Do you think the 3-union fields are interesting as a feature or we should
get rid of them completely?

I remember standing for them with perseverance, but now I start to doubt.
Maybe no one will ever use them. Maybe they are useless and a burden in

Do we get rid of them so the data handling get a bit easier?
Please comment on the backends you know, and your oppinion :)