If you want to keep making art, be my guest, but it's never going to happen. She's an adult, he's a kid. Think of the relationship the same as Mac and Frankie from Fosters Home for Imaginary Friends, he's 8 years old and she's 22 years old.
Right now, I'm shipping Spike with Emziko, because honestly it makes more sense than him be shipped with some pony. Plus, with a dragoness he can have kids of his own, and honestly, he deserves to have a family.
I always knew that Spike would outgrow his crush on Rarity, and The Last Problem pretty much showed that.