Why on earth would he say stop stop when the decision to stop or go is the captain's alone.
The
final decision is the PIC's alone as it is with every other decision.
Unlike the PIC failing to go arround when told by the FO at DA if not visual and the FO taking over, close to V1 there is an even smaller margin for delay.
Therefore our SOP is anyone can call "STOP" but the PIC can override that decision by using the command - "negative continue". This is a far quicker process (in both the GO and STOP situations) than FO calls problem, Captain thinks, decides and makes call and then FO does what expected.
Another issue is incapicitation. This is a very critical situation. If the PIC on a 3 eng aircraft has not noticed the failure of the number 2 10 knots prior to V1, do you want to pass V1 saying "what was that you said?" If the PIC has failed to notice the failure they are at that instant incapicated / not paying attention or what ever you want to call it.
Finally, please read the certification basis eg CS-25. Look at the time period involved in the most critical situation. Read carefully about the fact that this time must be increased if an action has to be called for. The A/C manufacturer needs to show evidence of using a realistic delay period appropriate to the situation of the FO calling a failure and the PIC making a decision. Has the manufacturer donw this with your aircraft? If so what extra time period have they used?
By using an SOP of PIC only calls stop, you effectively define the latest speed at which an emergency can be called by the FO and a decision made by the Capt and the FO makes the initial stopping action at V1. This speed will be quite some speed below V1 in an aircraft with rapid acceleration.
At the same time, the FO calls a problem just before he calls V1. How far above V1 will the aircraft be before the Capt decides to stop and takes the initial action?
I think that everyone is confusing the PIC having the final decision and the rejected / continued take-off procedure which has very closely defined time periods of things to be done if the scheduled performance is to be met.