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.
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.