[Pan-users] how should pan let users sort by active threads?

[Charles Kerr]

Right now the header pane's date column shows that row's article's date.
This is straightforward, but when sorting you get the date of the first
post in a thread.  But what if you're looking for active threads?
In that case, you really want to sort by the newest followup's date.

I'm leaning towards adding a second date column named "follow-up".
The good thing is that it's obvious how to use it.
The bad thing is that it's yet another column. :)

Can anyone think of a cleaner, but still obvious, way to do this?