It's a nice idea in theory, but I can see some difficulties that would need to be overcome.

Biggest is there is still competition on making easier hookups. Locking in the design would mean locking in today's inconveniences. I believe there is still room to make the hookup easier, no matter which brand we are talking about. I expect at some time to have a latching system fully controlled from the cab. No need to get out of the seat. Even the drive shaft could be attached and removed automatically if some thought was put into it.

Next, you have to look at changes going into the future. Would you make the interface strong enough for every potential head coming down the pipe? What if you had some sort of 24 row folding contraption? Would you set up various size categories similar to three point hitches?

Hydraulics are probably easy, but maybe someone wants to drive the knife by hydraulics off the combine rather than running all those belts and shafts to the front. Electrical hasn't stabilized yet enough to make a standard in my opinion. Maybe the head will be run by electrical motor in the future. Now you'll need a special harness that goes outside the standard.

I doubt any of my ideas are feasible. The point is that we are a long way from being ready to lock in a standard.