Actually, if you do a Google search for "Jenday Conure" and then go to Images, you'll see lots of them that look exactly the same as that bird, with all yellow heads and no eye-rings visible at all. So I'm going with it's a Jenday Conure...There is one sub-species of Brown-Throated Conure that also looks exactly the same except they have black beaks, and this guy has a white beak...
I hadn't ever really noticed any Conure/Jenday Conure without a white eye-ring before, but I wasn't every looking for one either. After looking at dozens of images of regular old Jenday Conures, not hybrids but just Jenday Conures, I'm pretty certain that's exactly what the bird in this photo is; it's a young bird, you can tell by it's eye being all black, so it might develop an eye-ring after it's first big molt when it's adult feathers come in.
The other dead-giveaway that it's a species of Conure is the texture of the yellow feathers on it's neck and head, if you look at it's neck and head and the feathers on them they look just like the neck and head of a Conure. So I don't think this is any big mystery or some other rare species of sub-species of parrot, or even some type of hybrid, I think it's just a young Jenday Conure...