Im just stating this idea.
Of course, Hasbro owns Rainbow Dash copyright, but Hasbro doesnt own blue ponies nor rainbow effects.
It won't be copyright infringement, if the courier was named something like:
Skittles the Pony
Also, the design of the courier does not have to be the EXACT Rainbow Dash.
It could be a horse/pony, the colour of the sky, with a rainbow mane, but like what someone else said above, have reins, straps, and even a chest box on its back.
This will not be copyright infringement, because Hasbro does not own Rainbows and Blue Ponies.
The design would be remotely similar, but it is an inspiration from Rainbow Dash, and can be classified as parody/satire.
Hence, it isnt infringement if someone can submit a Rainbow Mane Blue Pony as a courier design, and make this blue pony have blue wings and a rainbow hue when Speed Burst is used.
I would do it if I had the leet skills, but I dont. Sadly.
However, if this ever gets into Steam Workshop, I will ask everyone I know to like and favourite it and I will staunchly support it.
EDIT 1: Replying to Haters and Dissenters
Yes, MLP: FIM is a show targeted at 5-12 year old girls AND their parents.
It was intended as a show that parents can sit down and enjoy with their daughters.
Furthermore, I don't see why something that is targeted a a certain segment cannot be enjoyed by other groups of audiences.
1) This is like saying Dota is a computer game aimed at 15-30 year olds
, does that mean 10-14 year olds and 31 and above cannot and should not play them?
2) Lina is a fan service character of Lina Inverse, a manga/anime character.
Why is she in Dota 2 then? It is definitely Lina, because even her ultimate is named Laguna Blade, which should be black in colour, but due to Warcraft 3 limitations, became the default blue lightning.
3) Phantom Lancer is another fan service character of Kimahri Ronso from Final Fantasy X.
Why is he in the game too?
With these 2 extremely prominent examples, why is it that you guys are vehemently against a blue pony courier?
Its not entirely out of the Lore, and can be worded to fit it in.
It is also not infringing on copyright, because Hasbro DOES NOT OWN BLUE PONIES OR RAINBOW MANES. Hasbro only owns Rainbow Dash and My Little Pony.