Get Ansible to print lines for include_role(s)
I was able to create a custom callback plugin. I started with the default callback code and modified it:

    def v2_playbook_on_task_start(self, task, is_conditional):

        if(task._role is not None and task._role != self._current_role):
            self._current_role = task._role
            self._display.banner("ROLE [" + self._current_role.get_name() + "]", color=C.COLOR_DEBUG)

        self._task_start(task, prefix='TASK')


Now the output looks like:

ROLE [some_role] *****************************************************

TASK [some_role : I'm a task!] ***************************************
ok: [MACHINE]

TASK [some_role : Some other task!] **********************************
ok: [MACHINE]

ROLE [another_role] **************************************************

TASK [some_role : I'm a task!] ***************************************
ok: [MACHINE]


With the role line being bolded. It's a work in progress, but it at least makes it a lot more obvious where roles are being executed. My determination on block is that it is impossible to do what I wanted, due to the way the block class is implemented in Ansible.