elcruxio

That uninterrupted stress isnt't that big of a deal actually. You have the same kind of uninterrupted stress on your hands and feet as well. Sure you can switch hand positions, but the pressure is always going to be localized on the palm area of the hand. If there's too much stress there, there's nothing any amount of hand position swapping can do to alleviate it. Same thing with the feet, but usually you can't switch foot positions. As to uninterrupted, it's typically considered good form to stand and pedal every once in a while so you can get some pressure off the pelvic region.

I'll divide this latter part for hammocking curved saddles and noseless even though noseless saddles have options in both categories.

Curved.

1. You can, but it's generally not a good idea since sitting on the nose typically leads to pressure buildup on the soft tissues instead of bone structures. This can then interrupt blood flow and impinge nerves. Done too long and too frequently this can lead to permanent damage. The only time I'd consider sitting on the nose or "on the rivet" would be whilst sprinting since the pressure on the pelvic region is then diminished to a large degree.

2. You can but it depends on the shaping of the rear whether that's a viable option. However typically with curved saddles one tends to sit pretty far back anyways so going much farther back can result in the saddle running out.

3. Muscle workload is more related to pelvic angle and orientation. Moving back or forward can force changes in pelvic angle, but typically it's a better idea to learn how to lean back and forward to recruit different muscle groups. This is where curved saddles are at a disadvantage, because they usually lock one into a pretty static pelvic angle. Great for long distance riding because of the superb pelvic stability the locked in position provides. Not that great for racing though.
However if the curved saddle is setup for a racing orientation it can be just as good or even better than a flat traditional saddle for racing as then the locked in position is quite aggressive and aerodynamic.

Noseless.

1. You might not be able to move forward but with a noseless saddle you are typically able to tilt the pelvis forward to a high degree and far beyond what nosed saddles usually allow. Noseless saddles evolved from time trial and triathlon saddles meaning they take their design cues from saddles designed for the most aerodynamic positions possible. Needless to say this also works for high cadence.

2. Cutting off the nose doesn't need to alter the rear of the saddle desing in any way and usually it doesn't. Even ISM's have a typical rear saddle region where one can move to when climbing etc.

3. See point 2. There's no reason why this wouldn't be possible with a noseless saddle. You don't have the rivet position but in my opinion no casual rider actually needs that position anyways.
One the other hand the noseless desing allows for far larger pelvic angle variation when compared to the nosed saddle so in this regard the noseless saddle is superior.

Taking gear, bikefit or riding cues from the pro's is typically not a wise choice. Their realities are pretty different from that of a casual rider or even a semi serious racer. Pro's also don't usually choose their gear so that switching about the saddle can be just alleviating pain or numbness caused by a saddle that they did not choose and which doesn't fit well. The pro's also don't always care about their well being all that much so numbness or other discomfort is more than likely to be ignored by some in the pro peloton.

That being said, it is interesting to see that some pro teams are apparently switching over to noseless saddles. But really it depends largely on whether their sponsor makes noseless saddles and whether they are willing to provide them for typical road racing. In time trials nobody uses typical nosed saddles anymore.