Yeah I initially thought it could be Jason, but then I noticed when they were being questioned at the police station, Mr. Hastings ran into Jessica and then told her: "the police are asking questions about Spencer, do we still have an understanding?" Which leads me to believe she is protecting Alison's attempted killer not because she is protecting one of her children like we were all thinking, but because she has an agreement with Peter. Either way the Hastings are definitely hiding something big.
I've been thinking about another theory. If Ali wasn't sleeping with Ian and Ezra aka Board Shorts, and since Board Shorts and Beach Hottie are two different guys, we still don't know the identity of Beach Hottie. We were led to belive it could be Wilden, but I don't think so because CeCe apparently never met this guy and she definitely knew Wilden.
I'm thinking Beach Hottie is Wren, he already likes teenagers since he went after Spencer and then Hannah. He makes sense as being one of the A's too, Wren is a doctor and this season's A likes playing with body parts, has access to medical records, page 5, has money, works at radley, father had a mental illness so he could be a psycho too, plus both A and Wren drink vodka soda.
He is definitely not the ultimate A though, that may be the black widow.