Well, to start with he has absolutely stunning eyes, and he and Kevin made a lovely couple. The first really positive gay male relationship in a teen drama that I have seen. He might not be tied to the Coopers, but he is tied to the Serpents, who are still part of the show through the Jughead storyline at the moment.
Um, okay, those are reasons for wanting the character back, but why should they be reasons for wanting him to be Betty's long-lost brother?
The scene between FP and Alice after the party when he commented on her relative attractiveness then and now, and her being a former South Side resident, suggested a prior familiarity outside of just being at school together, and if Hal and Alice married before the baby was born then there would have been little reason for Hal to ask for an abortion or adoption, given his desire for Polly to have similar was down to Jason and not her age. Unless he suspected the baby wasn't his - and there is a passing resemblance between Raco and Ulrich, and the FP/Joaquin dynamic did seem a little paternal rather than just dynamic Boy Wonder to FP''s Batman.
Okay, I guess that answers my question, but it's still reaching. I think it's massively misunderstanding the scene to think that Alice was hiding so much from Betty. The whole point of the scene was that she decided to
stop keeping this massive secret and finally confide in her daughter about it. If the child had been illegitimate, that wouldn't have been any greater a source of shame to Alice than the fact that she gave him up for adoption in the first place. If she confessed the adoption, there's no reason she wouldn't have confessed the illegitimacy too.
It's not really that random. The show simply lacks characters who are in their twenties, hence Joaquin becomes the most likely suspect for Betty and Polly's lost brother by default as he's plausibly in the right age zone.
But new seasons usually bring in new characters and story arcs. We already know they're bringing in Hiram Lodge next year, for instance, and Roberto Aguirre-Sacasa has teased about the possibility of bringing in Sabrina, the Teenage Witch. He
also mentioned that Jughead finds a mentor at Southside High, so I take that to mean that will be a new recurring character too. So the lack of twenty-something characters in the
first season has no bearing at all on the availability of suitable characters in the second.
I say "plausibly" because we have no idea how old Joaquin is. There's no indication that he's a high school student... but conversely, there's no indication that he's not. The show's been silent on his age, and his relationship with Kevin isn't evidence either way.
As I said, given the heat the producers deservedly got over the "Ms. Grundy" thing, there's no way they'd do
another statutory-rape relationship between a teenager and an adult. Especially since it's a gay relationship that they were trying to present in a positive light -- they wouldn't want to taint it with illegality. So there's no way in hell that Joaquin is meant to be in his 20s. Besides, Joaquin wouldn't have been a credible infiltrator of this group of teenagers if he were an adult. Sure, to our eyes, they all look 20-something, but in-universe, the main characters are supposed to be 16, and it's generally pretty easy to tell a 16-year-old apart from a 22-year-old, say.
The
Riverdale Wiki says Joaquin is the youngest Serpent, and that he appears the same age as the main characters. I'd imagine that gangs like that generally recruit people in their teens.