In the interest of spreading the love for unpopular pairings, allow me to say a little but about Rayshipping (Ash x Cynthia)
What exactly is so appealing about this match? I'm none to sure on how old Cynthia is, but an older woman might be a good fit for Ash, namely one as experienced as Cynthia. Since Ash also makes a habit of taking part in so many different leagues, I think it stands to reason that one day he will be a champion himself. So, champion love :D
Furthermore, I think their personalities would match up nicely. Both seem to share the same philosophy on being a Pokemon trainer. Cynthia wouldn't fight with Ash non-stop, but she wouldn't be submissive either, and could actually put him in his place should he have a sudden bout of immaturity (which does happen to him from time to time)
While May and Dawn dream of being top coordinators and Misty wants to be a super special awesome water trainer, Ash and Cynthia share the dream of being Pokemon masters. One of them has already achieved that, so she could help Ash do the same.
Something else that is key: Cynthia is pretty hot, amirite?
If the two of them were to travel together, she would be able to fulfill Brock's role of being a map, cooking, and all that good survival jazz, while being able to provide analytical comments and passing on bits of experience (except Cynthia >>> Brock, so it would be even better). After all, she went on a journey once too, and travels on her own. She would also serve as the mandatory female traveling companion...except in terms of arse kicking, she is Brock and Dawn combined and then some.
Additionally, when Team Rocket comes around every other week with little more than a fake mustache, maybe Cynthia will realize something is up? One can only hope.
However, there are a number of points that might be made against this pairing. Let me address them.
1. Her position on Mudkipz remains unknown. While this is true, her position and reputation alone imply a level of knowledge that goes above and beyond what is normal, and even the average trainer knows lieks mudkipz.
2. She is too old! Well, so what? Age really isn't that big of a deal, especially as one approaches.reaches adulthood. I know it is common for men to go for younger women, and women for older men, but I see nothing wrong with going against the norm. In this instance, it could be both interesting and beneficial.
3. Ash and Cynthia can't be together because Ash and (x) are meant to be together! My response: NO U. Hypothetically speaking, anything is possible, especially if we're talking fanfiction, where the author is allowed to shape circumstance and make use of plot devices. I'm of the opinion that a good author can make any pairing work, and I've seen my share of more common pairings poorly executed, which further proves the point that the author is more important than how "canon" something is (I use the term canon very loosely)
Anyone have some thoughts to add?