The API window.show_quick_panel() has a parameter <selected_index> to open it with a preselected item.
However, if the index is after the first page of the lokkup (need the view to be scrolled), the view doesn’t scroll to this position (need to hit up/down to refresh it).
Just run this code in the console and hit up or down:
window.show_quick_panel([str(i) for i in range(100)], None, 0, 20)startup, version: 3054 windows x64 channel: dev
and latest version of ST2.