I posted this to Reddit, but there was no reception to it whatsoever.
I feel that there are enough inferences in the Anime to support this assertion.
For one, Misty appears to care for Ash on a level consistent with that of a parent taking care of their child.
For instance: After Ash's defeat at the Pokemon League, it was Misty who attempted to get Ash to leave his room.
Furthermore, that particular episode contrasts both Ash's and Misty's personalities, further cementing this relationship:
Misty is the rational one, trying to encourage Ash and stop him from moping; whereas Ash is emotional, pouty, and confrontational, all the characteristics embodied by a small child.
Secondly, there is an episode during the Johto arc, I don't remember which one though, where Ash gets lost. While looking for him, Misty remarks "Ash shouldn't get away from us" or something to that effect.
This serves to reinforce Misty's maternal concern for Ash.