Support for RTAI 5 has been merged into LinuxCNC 2.7 (and into the “master” development branch).
RTAI kernel packages are available for Debian Jessie, based on Linux 3.16.7 and RTAI 5.0-test1. At this time only i386 (686-pae) is supported, we’re still having trouble with amd64.
In order to use it, you need to install Jessie (i386) using the regular debian.org installer, add “deb http://linuxcnc.org jessie base” to your sources.list, install the linux-image and rtai-modules packages from there, and reboot.
There are debian packages of LinuxCNC available from the buildbot for this new platform, for 2.7 and master (the development branch).