The issue of P2 Takeoff is a bit complicated. The recommended training for it is called seat oriented. CM1 is trained to take decision and carry out the reject. The CM2 who becomes PF is only trained to do PM duties on a reject. So there's a role reversal at a critical time. Especially in a low speed reject where the full rudder and sliding the foot up for differential braking may be required any delay and excursion is a reality. In another real life incident Captain taking off in 737 at 114kts. his back rest collapsed and the backward movement caused throttles being pulled backed by 20% N1 which they didn't notice. He promptly handed over controls to copilot. Copilot not trained in PF duties in a reject just kept the aircraft straight. The V1 was 144kts correct decision for copilot trained to reject would have been to stop. The capt recovered, took over controls and carried out the take off but due to the reduced thrust aircraft got airborne beyond the available runway length hitting the boundary wall. Luckily they got away with minor damage. In my opinion copilot also needs to have ability to reject.