You can make the following REST call to get threads with a certrain status:
Given your example, the call you would make would be:
<#assign result =rest("/boards/id/myideas/threads/for/message_statuses/key/NewIdea/recent") />
I would have recommended you use /topics instead of /threads but it appears we only give you a count (and not the messages themselves) when you make a /topics /replies or /posts call.
It doesn't look like message status is indexed in the message search index, so the threads call is your only way to get these kinds of messages, at least for now.
-Doug
