So what's the lineup consist of? And are these straight up SST PVC's or Transformer crossover figures?
Yes, that gallery is from a Transformers website, but the only reason it's there is because the person reporting on Hasbro's Transformers Toyfair presentation just thought it was neat that Hasbro also has the Sesame Street license. There's no other connection.
And they're not what I'd call "straight up" PVCs. The figures are stylized—squished, really. A little like the Japanese practice of making chibi or super-deformed versions of characters, with oversized heads and small, compressed bodies. They're also similar to "baby" versions of the characters, although that's clearly not Hasbro's intention.
Otherwise, they are like PVCs: small, solid chunks of plastic with no moving parts.