Apple is in a somewhat different position to Qualcomm in that they were a founding member of ARM. I've also heard rumours that aarch64 was designed by apple and

Apple is in a somewhat different position to Qualcomm in that they were a founding member of ARM. I've also heard rumours that aarch64 was designed by apple and donated to ARM (hence why apple was so early to release an aarch64 processor). So I somewhat doubt ARM will be a position to sue them any time soon.