Hi -
1. It's certainly available, and it works. You can find lots of Google hits. For example:
http://www.dd-wrt.com/wiki/index.php/Asus_RT-N16
2. If you have a spare Asus RT-N16, why not just *try* dd-wrt?
You can always revert back - the link above tells you how.
3. Otherwise, if you're considering *buying* something - why not just get a Linksys instead?