Not only does he forget his grandsons name, when you deliver his parcel later he's like "It's great to see you player, you're already doing so well!" and then his grandson arrives and Oak is just like "Oh, yeah. Hi Blue. You're here too, I guess."
I remember after you beat the Pokemon League he's like "Grandson I'm disappointed. You clearly lost because your Pokemon hate you."
Like damn, Oak, that's cold. You're going to give that kid a complex.
Justice for Blue/Green/Gary/Fartass or whatever his name is supposed to be.
Funny you should say that, Blue actually goes through some character development in Gold/Silver/Crystal. You find him on Cinnabar where the whole island is gone now because of an eruption and he's sitting there like:
Like he's been humbled by the fact he was Champion for only a second. He's still snarky and a bit of a dick, but he noticeably loses gracefully.
And then fast forward to Sun and Moon and he's become buddies with Red and is way older and less of a jerk. Still competitive, but not egotistical.
I would adore them continuing that little story with them. I can just picture an older Blue acting as a kind of mentor for young trainers, the "lemme take you out and help get your first partner" kind. Not exactly a traditional Professor role, but keeping that passion as a trainer.
Could even have some fun with it, make some mentions to a quiet guy who comes around on occasion, and the two have a battle. Keep that connection between them.