Ben, this is more of a feature request than a question. Please submit feature requests here.

To answer a question in the comments below, you can always add the target="_blank" attribute to the link itself to open it in a new window. In the case of making a nav item open in a new window, the easiest way to do that would be to first make the page you want to open in a new window the last (or first) item in the navigation bar, and then targeting it with some liquid markup in the _nav.html file, located under Website > Theme > _nav.html.

In my example below, I am choosing to target the last item in the nav by using the {% if forloop.last %} tag and replacing this:

--------

{% if child.is_or_is_ancestor_of_current_page? %}<li class="active{% if forloop.first %}_left{% endif %} {{ child.slug }}">{% else %}<li class="nodrop {{ child.slug }}">{% endif %}
              <a href="{{ child.url }}">{{ child.name }}</a>
            </li>
          {% else %}
            {% if child.is_or_is_ancestor_of_current_page? %}<li class="active_drop{% if forloop.first %}_left{% endif %} {{ child.slug }}">{% else %}<li class="drop {{ child.slug }}">{% endif %}
              <a href="{{ child.url }}">{{ child.name }}</a>

-------->With this:

{% if child.is_or_is_ancestor_of_current_page? %}<li class="active{% if forloop.first %}_left{% endif %}">{% else %}<li class="nodrop">{% endif %}
<a href="{{ child.url }}" {% if forloop.last %}target="_blank"{% endif %}>{{ child.name }}</a>
</li>
{% else %}
{% if child.is_or_is_ancestor_of_current_page? %}<li class="active_drop{% if forloop.first %}_left{% endif %}">{% else %}<li class="drop">{% endif %}
<a href="{{ child.url }}" {% if forloop.last %}target="_blank"{% endif %}>{{ child.name }}</a>

---

Thanks.