This is nothing but a plot point. Before the recast, Kyle seemed turned off by all of Summer's advances.
But in light of this brewing paternity storyline, it creates more drama that Summer now wants to have sex with Kyle. I can see this turning into that Jill/Katherine/McKenzie/Billy storyline years ago, where Jill was running up and down Genoa City to prevent Mac and Billy from consummating their marriage, when it was thought that Jill was Katherine's daughter. lol.