I was going through ponychan merch section today, and I found a link to an area in which we can vote to get an extremely good chance at MLP lego. The reason I say really good chance is because they still need to secure a liscence agreement with Hasbro(ken) to even start. They still need to see support before then. 10k people need to support this, otherwise it'll fall through. Please go support lego derpy, she needs you so she can come to life! http://lego.cuusoo.com/ideas/view/11176#
Ah yes, saw this on EQD awhile ago. If this does get enough support I don't think that Hasbro would go for it as they have their own LEGO-ish brand, KRE-O. Currently it only has Transformers, but I wouldn't be surprised if they considered adding MLP to it as well.
I doubt that this'll ever come to life, since Hasbro's known for it's copyrights, and the chances of them giving Lego (a rival company) the rights to produce MLP lego toys is, if not 0, not above 1%. No matter what the fans say, they'll look at their profit, which'll be minimal seeing that they already produce MLP toys. It ain't impossible for them to produce Kre-o Ponies, but i also doubt that'll happen.
I personally prefer this guys Idea. Sets woul be better than just Ponies and the price ideas are AMAZING! http://lego.cuusoo.com/ideas/view/7568