The online advertising duopoly could become a threesome in just five years, with new research suggesting Amazon’s advertising business could soon be a force to be reckoned with. A notable trend over the past couple of years has seen vendors of all shapes and sizes buddying up to AWS in some way or another – so could now be the perfect time for players in the ad game to jump into bed with Amazon? “By 2021, we believe it is likely that advertising operating income will exceed AWS”, said a client note from Michael Olson, an analyst at investment banking firm Piper Jaffray. “Untapped potential” and “sleeping giant” have been common terms thrown around to describe Amazon’s advertising business in…