Why not eliminate power unit?

Hardware Vendors CUAV
1

Why not eliminate the power unit? or make it possible to choose from PMU power supply and ESC power. in this way, it may resolve the dangle of the power unit.

2

So, everybody should pay for integrated, redundant 5v
1 4s 2A power
Or
2: 12S 20A (also for servos)
Or
24S 10A for really big multirotors ?