I mean I've heard they're actually stoke about Dark Samus... they just were complacent when it came to Ridley and called him Captain America cause the rest of us were calling to too big BS to be just that, BS.
Though I don't care, I'd rather see them suffer and complain about not getting another FE rep than have them be happy about getting another FE rep... which is likely nonetheless.
While your reasoning for Adeleine is kinda solid, as a recent Porky supporter I'm just going to point out the following
1. Even if he's a joke, he's a major villain in Earthbound and Mother 3 so his absence is big nonetheless even if Giygas is not there either, Giygas could easily be in a Final Smash.
2. He is literally the /only/ boss throughout the entire series that doesn't have a spirit, I don't know about you but that in itself is to be equally suspicious as Sylux's absence is.
3. Next year happens to be Mother's 30th anniversary and while I'm not saying anything will happen, it would make a ton of sense to add one of the series' major villains and characters there alongside either Mother 3 finally being given to everyone outside of Japan or a remastered Mother 3 and Earthbound game in 3-D.
Nonetheless I'm gonna stop it there as this is the /Sylux/ thread, not the /Porky/ thread, I just had the urge that had to be said and not be left alone.
I still do believe out of everyone though Sylux has the biggest chances since he's a pre-established character that could be a promotional fighter for an upcoming game that's highly anticipated by fans, I do think though he'll be in the latter said of DLC since I view Prime 4 releasing late 2019 or Early 2020. Porky is the second for reasons I've stated, and Adeleine is the third and least likely due to what you've said but she's also a popular character in the Kirby fan base and has been requested to return for years on end and she finally has with Star Allies so that is something to note and K Rool and Ridley having similar requests is finally what got Nintendo to add them to the roster (as if I recall with K Rool, apparently they were surprised how much he was requested to be in Smash Bros.) so I don't think Sakurai's vendetta against her would stop her from appearing alone as you said. The man also hasn't worked on a Kirby game for years he could've just passed by her not even knowing or remembering her, if anything I think Adeleine could at the least be a future DLC spirit (personally if you had asked me before we knew all the assist trophies I would've said she'd be a lock but uh... Vince took that spot, so... that could either decrease or increase her chances if you ask me). Nonetheless if spirits and bosses do deconfirm (I say bosses because I know 90% of the community will shrug off Bowser turning into Giga Bowser and
because "They're veterans, they don't break the rule") she's the only plausible Kirby rep in my eyes that could be DLC unless they somehow make Zero II of all things a playable fighter or Hyness from Star Allies.