Nop, they will never do that. Have you looked around the internet? Almost everybody have a pony oc of some sort... The cost to sue every single person for having an oc would get miraculously high and they would gain a very very bad reputation and lose customers. That is something Hasbro do not want to do, if anything they want to stay on everyones good side to ensure that people will keep buying their products.
Just because you heard of something sooner than something else dont mean it really came first. My OC have existed since about 3 years back, she she was around earlier than Sunset. I also was not accusing Hasbro of copying her, I was joking because for some reason, they do look alike.