The end product ATP would end up outside because in a plant cell it is used in the Calvin cycle.
Work Step by Step
The enlargement of the thylakoid membrane would show a high H+ concentration in the thylakoid space within the membrane. The ATP synthase would be integral, poking out on both ends of the membrane. The outside should have a lower H+ concentration. ATP is synthesized in ATP synthase as it uses the H+ gradient to do work, specifically by allowing some H+ to enter into the thylakoid space.