I think it'd be nice to have a non-threadsafe controller available. 

What I mean, is being able to group a set of requests so that only one thread at
a time would be able to execute them in sequence.

For example, if I'm scripting an action to reassign a bug and there's a
confirmation page, it's possible that two threads could reassign the bug at the
same time to different people, which would break my final results assertions. If
I had a non-threadsafe controller available, I could put the reassign, confirm,
and verify requests inside it and always get predictable results.

I realize it would mean making other threads wait and could bottleneck a large
test, but I think if a controller like this is used responsibly (ie, to group
very small sets of atomic actions) it could be a great help.