I'm not sure your point here is that from a technical IT perspective this would have been more manageable if the Government were to chunk up the enrollment process. It might be the case that a nationwide rollout was required by the dictates of the legislation or principles of public fairness to all. As you probably know, Government IT work, especially a rollout of this magnitude, is generally staffed 90 percent Government contractor (and generally giants in the IT contracting world including a number of Fortune 100 companies) and 10 percent Federal employee (generally Federal managers). I'm not sure Government really works that much differently than the private sector, but the technical and public issues are somewhat daunting to those who merely navigate in the private sector. I say this not to blunt richly deserved criticism for the glitches, but to point out that the Government generally relies on a lot of contractors (from the private sector) to perform this type of work.
From a distance, the idea of rolling out on 10/1 in, let's say Delaware, Arkansas, and Wyoming as a pilot and them slowly spread across the country with 3-4 new states every few days might have avoided a lot of the issues. I'd expected massive interest from the press and from simple onlookers.
You're probably right .... Likely it was written in such a way as to require full rollout at the same time.