Yes! It’s what we deserved! It’s what THEY all deserved.
I honestly pick Neville over Cedric (though I love Cedric!) because I really, really, REALLY, love Neville and his arc. I think it’s so interesting to have both Harry and Neville as options for The Boy Who Lived, as two sides of the same coin, one who starts out curious and a little reckless and brave (Harry) and one who grows into his confidence and bravery (Neville). I also think they each ended up with terrible home lives as children because of Voldemort and how they would react to that as they continue to process it as adults and heal together is really interesting to me. Neville would continue to grow into his confidence with gentleness and Harry would benefit so much from seeing that gentleness and patience have everything to do with being curious and brave, too, and it would maybe help temper his (completely understandable) anger. And Neville might have room to be more angry with Harry. Not angry, maybe, but that it’s okay to say hey, these terrible things happened and I can be mad about them. (I have more here but I will stop. I just love them so much!)
As for Sirius’ talk, he’s going to do it even though it’s Neville and we think Neville wouldn’t hurt a fly but that dude also pulled the sword of Gryffindor and lopped off the head of a snake while defying Voldemort to his face, so. Moral of the story is Neville is awesome but you still have to cover your bases. It would involve some logistical talk about sex, which will mortify Neville first hand and Harry second hand. It will also go into detail about what Harry really needs is someone to help him take care of himself because the Dursleys and Dumbledore kind of instilled the opposite. And how Sirius knows Neville wants to do the right thing here. But Sirius is always going to have Harry’s back in a fight, even if he’s wrong. Just so Neville knows. It would also end with a box of condoms and a very red faced Neville.
Later, when they are both professors at Hogwarts because with Neville Harry realizes he doesn’t have to keep proving himself over and over and can just be and do what he wants, Sirius will visit and absolutely make a mess in Neville’s greenhouses (Sirius is brilliant and was good at Herbology but it’s not his thing). Neville will indulge this for a while but then send him Harry’s way and Sirius will want to teach his students all kinds of spells he shouldn’t and so finally Harry sends him to their quarters and Sirius amuses himself poking around until they are ready to have dinner, and then they nip down to Hogsmeade and enjoy each other’s company.