I actually like the idea of Ash liking a girl who was a recurring and his rival could also like her and she could be not interested in both or just not aware. I rather the girl be not in the main group or a rival because then it would either be all the time or them busy bickering. Which I don't want to see. I want to see Ash crush over a girl for a change and another guy crush over her for a change. That would be fun.
But it won't make the show as interest as Love triangle between Ash , A referring female character & A Male Rival would made .