I don't think they did. They always seemed to have a note of pessimism - like the famous quote: "A republic, if you can keep it". George Washington handing off power peacefully was a big deal. It was all a huge experiment, and there was fierce debate from the very beginning as to how to best proceed.

I think their vision and planning was astonishingly resilient. Indeed, I don't believe you could found a government with more longevity and corruption resilience; ultimately, that must come down to the people and their willingness to maintain a corruption-free government. No amount of thinking can come up with a system that will self regulate regardless of whether or not the populace is paying attention or cares.

The other big thing is technology. They knew human nature and politics well, but technological shifts have repeatedly flipped the table and completely changed power dynamics. The amount of personal power over others that a single person can have thanks to technology has dramatically skyrocketed since then.

I think they expected some kinds of major technological improvements, and similarly expected (or intended for) government to be more proactive and change laws and even the constitution a lot more; tweaking to reach and maintain maximum efficiency.