I'm always open to new ideas and suggestions. I'm sure, however, that I won't get around to doing it before the 9th of June.
But I do have two questions: What do you mean by "next message"? The normal view of a message thread is the hierarchical tree view and it is not entirely clear what "next" means in such a context. There are several ways to traverse a tree ... But I suspect that you mean "next" ion a chronological sense, like the messages are ordered in the linear "All" view. Is this the case?
The second question would be, if "next" is meant chrononologically, then there is the "All" view. So it would be a short-cut to represent the "All" view one message after the other, right?