Actually, he didn't, because both ends of that hose are on the high side of the pump. If the hose flowed even a little, it would either be moving the very hottest coolant to the rear port, or it would be moving cool coolant away from the rear and into the radiator. The one thing it absolutely wouldn't accomplish is to add cool fluid to the rear. I'm guessing that only a small amount of coolant actually flows through that hose, and only when the thermostat is closed.
This is different from the mod in the youtube video, because in the video, the rear port is connected directly to the water pump outlet. That would have the effect of diverting a bit more flow to the rear of the block.
As I explained, the temp swings are an inevitable consequence of having the thermostat on the cool side. The thermostat has to be slow-reacting, or the system wouldn't work at all. You can produce more stable temperatures by engaging the fans earlier, but it's tough to get temps rock steady.
I think what you're looking for here is a strategic flow approach, as has been attempted on some Jaguar engines. This entailed sizing the ports in the head to restrict flow to the front cylinders, which allows more flow to the rear. It can be accomplished with a special head gasket, so it's possible to work out a retrofit. But this hose is just ludicrous.
Many modern cars use MAP controlled thermostats, where the "natural" temperature of the thermostat is 240F, and it's artificially heated with a resistance coil. This allows the ECU to implement a dynamic temperature range that's correct for each operating condition. "Normal" may be anywhere from 170-240F. So no gauges for you.
Personally, I prefer a steady temperature, as fluctuating temperature means fluctuating pressure, which eventually fatigues the radiator and heater core. But that's not where things are going.
97: I can't put my finger on the flow diagram at the moment. Coolant enters a blending chamber from the bypass, heater return and radiator. This is where the thermostat lives, reacting to the blended temp. From there it enters the pump inlet, and is pumped into a gallery along the right side of the block, and from there distributed through the block and head. The block drain is on the right side water gallery, all the way at the back. Here's the blend chamber:
