Since Ash's Charizard has formally rejoined his team, and it has been announced that the bridge series will take place on an island chain much like the Orange Islands, I can see a return of Lapras as very likely. Also, with speculation that Ash may release fan-favorite Oshawott, it's exceedingly likely that former Kanto members of Ash's team make reappearances, as oppose to him catching new pokemon.