You can all thank Kordanor for the following information, Apparently the latest Spiderweb Software's newsletter confirms Avernum 2: Crystal Souls is in development.
More information.
I'm sorry I can't find any more information beside this right now. I will be sure to keep you all updated on any news from SpiderWeb, or other sites in the future.We have already begun work on our ground-up rewrite of Avernum 2. In the same manner as Avernum: Escape From the Pit, Avernum 2: Crystal Souls will be a fresh, expanded reworking of one of our most beloved titles. Hopefully, it will be out for Windows, Mac, and portables before the end of 2014. When we have an official announcement, you can find out right away on our Facebook page.
More information.