Display old entry version content through twig?
Probably something very similar to what Craft does when displaying past entry revisions from a template in the control panel. :)

https://github.com/craftcms/cms/tree/master-v2/src/templates/entries/_revisions.html#L23-L36

{% if section.enableVersioning %}
    {% set versions = craft.entryRevisions.getVersionsByEntryId(entry.id, entry.locale) %}
    {% if versions %}
        &lt;h6&gt;{{ "Recent Versions"|t }}&lt;/h6&gt;
        &lt;ul class="padded"&gt;
            {% for version in versions %}
                &lt;li&gt;&lt;a{% if entry.getClassHandle() == 'EntryVersion' and version.versionId == versionId %} class="sel"{% endif %} href="{{ url(baseUrl~'versions/'~version.versionId) }}"&gt;
                    {{ "Version {num}"|t({ num: version.num }) }}
                    &lt;span class="light"&gt;{{ version.dateCreated.uiTimestamp() }}, {{ version.creator }}&lt;/span&gt;
                &lt;/a&gt;&lt;/li&gt;
            {% endfor %}
        &lt;/ul&gt;
    {% endif %}
{% endif %}