Well one of my friend did.Many people say that its random and is not actually dependent upon how many views you have got till far because many big writers haven't got invited.But what I understood you are invited taking regard of all the things quora has like if you break certain terms and policies then Quora Moderation will send you a message.Well try to be safe from that because quora is strict on those cases .But another thing it's not only about views bit also the quality of answers matter as well and how many upvotes you are getting.Sometimes they can check how active you are in quora.These are my opinions ,quora themselves have never declared these things that who they invite to quora partner program but I believe the above said things could be one of the reasons to get invited.