I have 1600+ rifts completed. Have only had the cow rift once. I don't fully understand why blizz decided to make it so rare? You don't even get that much XP from it and don't really get any reward?? Not sure how much XP you get from it, but even if it gave you 25bil experience or more?..in the end that's not that much at all compared to the paragon level system.
My second point though..why does blizz not add more things like this? There could be plenty of special and fun events they could add into the randomness of rifts.
Regular Shrine/chest events..should already be in them.
Special shrine/chest event.
Mini boss's in the rifts at randomness
Random Mini games? I'm sure there could be some fun quick possible ideas with this.
Blood shard rift? This is one that would fall under very rare occasions. (once every 100-200 rifts?)
Buff experience rifts(200%) thru out the whole rift.
Legendary buff rifts(X%) thru out the whole rift. Once again this would be on the very rare occasions. (Once every 100-200 rifts?)
I'm sure there are plenty of other ideas. My best guess is, blizzard hasn't done anything like this because it will kill the Grift system. But IMO, I'm not a big fan of the grifts. Not that there all that bad, but because there is no reward at the end. Nothing changes with the loot the higher you go, you just get more of the same crappy legendarys 90% of the time. Once you level your gems high enough it is almost impossible to go higher. Doesn't take to long to reach that point. For me, I'm not a leader board person in D3, because once again no rewards? So IMO leader boards mean nothing.
I'm not trying to bash here or anything. Just throwing out some ideas and my opinion on the game, in some areas I think could be improved on.
I had the second level of a rift in Whimseyshire. I was excited because I assumed I would get the achieve for killing Lord of the Bells. As it was the second level, I was going to pop the RG there. Instead, Bone Warlock was the RG that spawned. That's when I realized that the Whimseyshire and Cow levels were not the same thing =(