Theoretically, if given unlimited inspection time before an attempt, would it be possible to plan an entire solve? If not, how much of a solve do you'll think is possible to plan without touching the cube?
Yes, it is. SpeedBLD is an unofficial event where you plan the whole solution with a speedsolving by inspecting and without turns. The UWR is 6.46 by Rami Sbahi, and he took an hour to memorize the solution.
Theoretically, if given unlimited inspection time before an attempt, would it be possible to plan an entire solve? If not, how much of a solve do you'll think is possible to plan without touching the cube?
Without touching the cube at all? That means one side of the cube would not be visible, meaning some scrambles would be impossible to completely predict (for example, if the all of the yellow edges are on the bottom, with only yellow visible on all of them, they could be permuted relative to each other, or an EPLL away). A lot (probably a majority) of scrambles could theoretically be planned ahead to the solved state without touching the cube at all though.