This has been proved by Szekeres & Peters (2006). They carried out a computer search which eliminated all possible configurations of 17 points without convex hexagons while examining only a tiny fraction of all configurations. Szekeres, G.; Peters, L. (2006), "Computer solution to the 17-point Erdős-Szekeres problem", ANZIAM Journal, 48 (2): 151–164, doi:10.1017/S144618110000300X