Many years could have been the year of Juan Martin del Potro. So many of them weren’t. This, in part, explains why rooting for this 6-foot-6 lunk remains such an appealing proposition to so many: none of the buttery mundanity of rooting for Federer, none of the monotony of hyping up a Nadal or Djokovic who’ve already enjoyed their soul-crushing runs of dominance with double-digit major haul. It is instead rooting for someone whose gifts explode off the television screen but who remains, in some sense, unproven. Much of that Delpo appeal is that faint air of melancholy, the whiff of what-if. What if his wrists hadn’t failed him? But they did. Now his every gesture reads as impossibly soulful. The hugs (of linespeople, of injured opponents), even the protests (of his own errors, o…