If Congress passed a bill that was national, injected significant startup funds, and guaranteed the lowest possible rates, the result would come pretty darn close to a public option. Sure, a true government-run public option would be able to mandate payment reforms like paying for health care "episodes" rather than individual hospital visits. A public option could also avoid many of the startup costs by building on the pre-existing Medicare infrastructure, which already has relationships with doctors and hospitals. (Also, keep in mind this is all separate from the question of how actually to pay for health care reform.) But those features also happen to be the ones that scare conservatives most—namely, the government's ability essentially to mandate reforms in the private sector and the looming threat of single-payer Medicare for all.
At the same time, a cooperative would be more flexible than a public option. It wouldn't be subject to government salaries or hiring practices and would be able to tweak its offerings relatively quickly. (By contrast, it took the government 35 years to include prescription drugs in Medicare.) Perhaps the greatest advantage of a cooperative is simply what it's called. If it's not called a "public option," Republicans can claim victory. But if it provides most of the benefits of a "public option," so can Democrats.