Defense Grid 2 is now happening thanks to a private investor and it will even be coming to Linux in 2014!
Hidden Path Entertainment did a Kickstarter last year that sadly hit no way near it's goal for a sequel, even though the Kickstarter was successful for an expansion to the original (Not on Linux).
Thankfully they have updated everyone on the good news of the Sequel!
On their news post from the 25th it states:
QuoteNow, it is pleased to announce that the Defense Grid community helped catch the eye of an investor and DG2 is successfully being developed.
Great news for Linux gamers as their official website for Defense Grid 2 states Linux support!
QuoteComing in the first half of 2014 to Steam for Windows, Macintosh & Linux
Good news eh!
For reference here is a video of the original: