Hi Maciej,
I think the Hql/Sql activity is intended to used by developers. People who want to use these activities should be familiar with how to write a hql/sql query. And they must know the database structures.
So the developer-oriented activities could expose all of operations that hql/sql could do. Not only select, but also update/insert/delete.
In my opinion, if we provide this feature in jBPM 4, it will be only used by developer, not end-user. So I think we could wait for other people's advices. :)