Is Starting the ICE at 50 MPH ok?

It is certainly possible to have the ICE at idle speeds at 50 MPH.
The ICE is pampered by a 'starter' that brings it up to idle speeeds aaand leets oil pressure build before applying spark.

 

I can't imagine that Toyota could have not thought about that possibility when they designed the software system. I'm sure this was an expected scenario.

Whenever my ICE is first activated (at any speed) the EV system appears to still be the main source of power for the car. I see EV range drop as if the gas engine is just warming up slowly (which I believe is best for the engine).

 

No matter what you do, the engine will always warm up gracefully. The system is very well thought out, always taking emissions & longevity into account.

Watching a ScanGauge, it's easy to confirm that. I see the engine running at a lower than usual RPM while the coolant temperature is still low.

Watching the EV capacity, you'll see it drop initially... dipping well into the HV capacity if EV is already depleted entirely to ensure the engine isn't worked too hard.

So regardless of speed, power, or temperature, when the engine warms, it is protected from wear... much like it has been for startup itself for over a demand. The battery-pack is taken advantage, rather than putting stress on the engine.

 

Don't forget ... 'back-in-the-day' - oil was thicker too. 30w oil was the norm for decades. Now? 0w-20 goes in the Prius. Thin/light viscosity makes for easier going. That said, yes, the Prius is designed to take off 1st ... and warm up on the fly. Now if it's 20 below outside, you MAY simply wana do a start-up ahead of time so YOU'RE warm, once you're ready to jump into your ride. And collaterally, the Prius will be warmer too.

.

 

Not a problem. ICE will start and it'll actually slow down MG1 from revving from 7,600 to 4,000 rpm.