If you had stopped playing during the lull of content with 3.0, you could come back on, do the Void Ark, new dungeons, MSQ and Lords of Verminion challenges. Pretty much everything 3.1 has to offer, other than the Diadem (which is garbage anyhow if you're not interested in gear) and Thordan. You could do Thordan too I suppose, if you knew people who still play. Besides, that's the entire point. They're not meant to get into gear progression, it's meant to entice them into subscribing.
I'm sure they would have missed the 2-3 emails they send about it, along with the email(s) about the campaign.