Is it possible to use a lightswitch (or something similar) for different post types?
I think your answer is in the post you referenced. Create two entry types in a single section, each of which contains different fields (and/or some in common). Then loop through all the entries and test for entry type in the output.

{% set entries = craft.entries.section('blog').find() %}

{% for entry in entries %}
    {% if entry.type ==  'linklist' %}
        &lt;h1&gt;&lt;a href="{{ entry.externalLink }}"&gt;{{ entry.title }}&lt;/a&gt;&lt;/h1&gt;
    {% else %}
        &lt;h1&gt;&lt;a href="{{ entry.url }}"&gt;{{ entry.title }}&lt;/a&gt;&lt;/h1&gt;
    {% endif %}

    {{entry.body }

{% endfor %}


The user will have to understand how to change the entry type in Craft's UI (it's the dropdown in the right column, but it's pretty clear once they've been shown how to do it once).