On October 25th Asterisk 11 has been officially released. It seems to be working well on the RPi so far. If you want to give it a try, install it with:
apt-get update apt-get install asterisk11 freepbx
The latter will also install the latest FreePBX version 2.11.0beta1, which is compatible with Asterisk 11. The Asterisk package contains version 11.0.1. After installing the packages above, you will get continuous updates with apt-get dist-upgrade in the future.
To make the commands above work, you need to have the latest version from the downloads page, or at least the September version with upgrades installed.
Asterisk 11 and the latest FreePBX is still to be tested on the RPi. If you like to join the testing, your results and comments are highly appreciated!
P.S.: When upgrading from Asterisk 11.0.0 with apt-get dist-upgrade run
apt-get -f install
to fix some changed dependencies in the new Asterisk 11 packages.