I have been working on a design for BL Touch for the I3 Mega. Something that adds on to the existing hot end carriage with little to no modification. I have added two different designs. One that places the sensor in front in line with the nozzle and the second that places the sensor on the side near the front to avoid X axis interference. This will allow full X travel and wont hit the frame. I haven't printed or tested this yet so feel free to give feedback.
3/16/19 Simplified. It didn't need to be so "robust".