Is it viable to use a Pinion gearbox system / internal gear hub / CVT gears for a road bike?

Just a thought I had What would be the top speed if I ever sprinted using one of these?

The top speed is way over 100 km/h, probably at least 150 km/h.

The process for obtaining such unbelievably high speed is as follows:

1. You start sprinting
2. The rear hub fails to withstand the high torque
3. You fall
4. A witness calls ambulance
5. The ambulance arrives, transports you to the hospital, and this is how you obtain the >100 km/h speed

For example, Rohloff speedhub, the 14-speed internal gear hub, supports with standard sized chainring and sprocket only 250 Nm torque at the cranks.

On a road bike, in sprinting position, the handlebar allows you to obtain extra leverage. Maybe 30 kgf of extra force.

The clipless pedals allow you to pull up with the rear pedal and simultaneously push with the front pedal. Maybe 25 kgf + 25 kgf = 50 kgf of extra force.

This is added to your weight. For example, if you weigh 80 kg, it's 80 kgf of force.

So I already see 30 + 25 + 25 + 80 kgf = 160 kgf = 1569 N.

If the crank is 175mm long, this is 0.175 m * 1569 N = 275 Nm, over what the Rohloff speedhub can withstand using standard sized chainring and sprocket.

Rohloff speedhub is not the only one at fault. There are internally geared hubs that suffer from even more severe problems at lower torques, such as the Sturmey Archer 3-speed hub.

Priority Bicycles offers both a Pinion Gearbox Road Bike with a 600% gear range and a CVT Road Bike with a 380% gear range.

I recently purchased the CVT and find it suits my needs. I have on occasion wished for both lower and higher gearing availability but generally I'm not climbing killer hills or trying for speed records.

Sequential gearing (or gear equivalent on the CVT) is very convenient. So too is the ability to shift without pedaling while stopped, although the top and bottom 15% of the CVT requires pedaling.

I can't answer the Top Speed question, it makes me flash to the very old car commercial that specifies top speed as "Down hill in a hurricane". If top speed is an important factor, I would suspect the CVT would not have a range to satisfy you. The Pinion probably would, but it's not inexpensive.

You could use any of those options, but they will all absorb more of the input energy compared to traditional chain and derailleur gearing. This will reduce your output speed or distance by comparison.