At the last scene of Till We Compete Again! when Ash is shown entering his house the white flowers in the foreground are Baby Breath flowers which symbolize everlasting love. It's a hint from the writers that shows their content with the ending of XY&Z having Ash and Serena kiss.
The flight Serena was going to board to head to Hoenn was H71 Latias. "H71" can be interpreted as the #071 in the Hoenn Pokédex, which is Mawile, or Kucheet (クチート) in Japanese. This can be read as a corruption of 口と, meaning "with the mouth", suggesting that Serena kissed Ash on the mouth.