Exception Annotations: Lay of the Land

At the risk of confusing myself and others (this is full of subtle issues!)

Suppose we made the toException of both SomeException and ExceptionWithContext actually respect the “produce a SomeException with no attached ExceptionContext” invariant. No exceptions (pun accidental) for it!

Suppose as well that we add a separate toExceptionPreservingContext :: ExceptionWithContext e -> SomeException function, and also redefine rethrowIO as

rethrowIO :: Exception e => ExceptionWithContext e -> IO a
rethrowIO e = throwIO (NoBacktrace (toExceptionPreservingContext e))

Would that work / bet better? Instance definitions would be more uniform, at least.