Arri just announced an upgrade to allow internal ARRIRAW recording, using an XR module that replaces the existing SxS card holder. It will only add 8mm to the width of the camera.
The XR drives will record 55 minutes of ARRIRAW at 24fps, be able to record up to 120 fps, and have a data rate of 6.7 Gigabits per second. An adapter will still allow for SxS PRO cards to be used for ProRes.
A new Alexa XT range will have the module built-in, all with 4:3 sensors.