I just succeeded in getting Bluetooth working on Nexus 7 with Plasma Active. In order to get Bluetooth running you need the latest kernel from the hardware adaptation repository and install the new “nexus7-fw-installer” package, which can also be found in the Nexus 7 hardware adaptation repository. In case you are using a permanently flashed kernel please make sure to also flash the new zImage.
After the “nexus7-fw-installer” package was installed you will need to run “nexus7-fw-install” as root. This will download the required proprietary firmware bits and will help you during the installation. Please note that you need to accept (and of course read beforehand) the displayed license in order to install the firmware. For more information follow the displayed instructions.
Also thanks to the Ubuntu guys who provided great information on how to get Bluetooth running on Nexus 7.
Edit: After the installation has finished you should reboot once to get everything working.