3- If the PI System Demo shows the current state of the Solution, then who...

The PI System Demo is a significant event that provides an integrated view of new Features for the most recent Iteration delivered by all the teams in the Agile Release Train (ART). Each demo gives ART stakeholders an objective measure of progress during a Program Increment (PI). A system demo is a critical event. It’s the method for assessing the Solution’s current state and gathering immediate, Agile Release Train -level feedback from the people doing the work, as well as critical feedback from Business Owners, sponsors, stakeholders, and customers. The feedback is critical, as only they can give the guidance the ART needs to stay on course or make adjustments. Therefore, the system demo is intended for the Business Owners, who are key stakeholders that have the ultimate responsibility for the Return on Investment (ROI) of the solution1. References: System Demo - Scaled Agile Framework