So, just out of curiosity, I tried importing some old comments. And it kind of worked.
http://thefpl.us/beta/episode/151#disqus_threadAs you can see, I got the old comments with the old datestamps in there (but without the votes), which is kind of cool, but it shits the bed once it runs into HTML formatting.
If you're curious, here's the XML file I wrote.
<?xml version="1.0" encoding="UTF-8"?>
<rss version="2.0"
xmlns:content="http://purl.org/rss/1.0/modules/content/"
xmlns:dsq="http://www.disqus.com/"
xmlns:dc="http://purl.org/dc/elements/1.1/"
xmlns:wp="http://wordpress.org/export/1.0/"
>
<channel>
<item>
<!-- title of article -->
<title>F Plus Sings!</title>
<!-- absolute URI to article -->
<link>http://thefpl.us/beta/episode/151</link>
<!-- value used within disqus_identifier; usually internal identifier of article -->
<dsq:thread_identifier>episode/151</dsq:thread_identifier>
<!-- creation date of thread (article), in GMT. Must be YYYY-MM-DD HH:MM:SS 24-hour format. -->
<wp:post_date_gmt>2014-09-13 13:39:00</wp:post_date_gmt>
<!-- open/closed values are acceptable -->
<wp:comment_status>open</wp:comment_status>
<wp:comment>
<!-- internal id of comment -->
<wp:comment_id>1</wp:comment_id>
<!-- author display name -->
<wp:comment_author>CuddleWEEDLYWEEDLY</wp:comment_author>
<!-- comment datetime, in GMT. Must be YYYY-MM-DD HH:MM:SS 24-hour format. -->
<wp:comment_date_gmt>2014-09-13 17:52:00</wp:comment_date_gmt>
<!-- comment body; use cdata; html allowed (though will be formatted to DISQUS specs) -->
<wp:comment_content>o/~ ANTS ON KITCHEN COUNTER! o/~</wp:comment_content>
<!-- is this comment approved? 0/1 -->
<wp:comment_approved>1</wp:comment_approved>
</wp:comment>
<wp:comment>
<!-- internal id of comment -->
<wp:comment_id>2</wp:comment_id>
<!-- author display name -->
<wp:comment_author>Miles Beavis</wp:comment_author>
<!-- comment datetime, in GMT. Must be YYYY-MM-DD HH:MM:SS 24-hour format. -->
<wp:comment_date_gmt>2014-09-13 18:08:00</wp:comment_date_gmt>
<!-- comment body; use cdata; html allowed (though will be formatted to DISQUS specs) -->
<wp:comment_content>It's a crying shame that Jimmyfranks didn't get a verse in "No Sex". THANKS, STOG. >:(</wp:comment_content>
<!-- is this comment approved? 0/1 -->
<wp:comment_approved>1</wp:comment_approved>
</wp:comment>
<wp:comment>
<!-- internal id of comment -->
<wp:comment_id>3</wp:comment_id>
<!-- author display name -->
<wp:comment_author>Djw175</wp:comment_author>
<!-- comment datetime, in GMT. Must be YYYY-MM-DD HH:MM:SS 24-hour format. -->
<wp:comment_date_gmt>2014-09-13 18:27:00</wp:comment_date_gmt>
<!-- comment body; use cdata; html allowed (though will be formatted to DISQUS specs) -->
<wp:comment_content><![CDATA[Since I'm tonedeaf, I won't participate in the remix, buy I did hear one of my keywords!<br><br><img class="img" src="http://i.imgur.com/waBvuk8.png" alt="" border="0"><br><br>This is an unholy amalgamation of four different kickstarters I used for references. I used that creator picture because it just looked so happy! And those numbers are from an actual music kickstarter I found. The person wants $2k to record some hip-hop stuff.inspired by "10 years of music exploration".The creators age? 23]]></wp:comment_content>
<!-- is this comment approved? 0/1 -->
<wp:comment_approved>1</wp:comment_approved>
</wp:comment>
<wp:comment>
<!-- internal id of comment -->
<wp:comment_id>9</wp:comment_id>
<!-- author display name -->
<wp:comment_author>Bob Johnson</wp:comment_author>
<!-- comment datetime, in GMT. Must be YYYY-MM-DD HH:MM:SS 24-hour format. -->
<wp:comment_date_gmt>2014-09-14 19:47:00</wp:comment_date_gmt>
<!-- comment body; use cdata; html allowed (though will be formatted to DISQUS specs) -->
<wp:comment_content>PARTY PARTY PARTY PARTY PARTY PARTY</wp:comment_content>
<!-- is this comment approved? 0/1 -->
<wp:comment_approved>1</wp:comment_approved>
</wp:comment>
</item>
</channel>
</rss>