...Actually, about that...
I'm surprised I haven't touched this response yet.
Sorry, but no. A kiss doesn't make anything canon. Ash probably is still the dummy we all know and love, who's also a Pokemon Battle Prodigy. Basically now how the Alolan Shippings of Ash x Lillie, Ash x Lana, and Ash x Mallow have already caused a somewhat competition between new viewers, there's really no reason for Serena to be here, since she's doing her own thing. Not to mention, Serena kissing Ash was likely her way of releasing this built up momentum that had been growing of XY and XYZ to give Amourshippers a good conclusion, which if I step into their shoes for a second, both makes a lot of sense, and would satisfy the average fan.