Oh yeah Platinum was great just due to how much more fleshed out of a overall game it was when compared to Diamond and Pearl, tbh it's actually one of my favorite games in the series now haha.
Actually I can see that now too to an extent, seeing random trainers progress to gym after gym and at some point you would hear from them again as they would request to see you at the Pokemon League but what I'm wondering is what will happen if they end up winning against you, would you demand a rematch to reclaim your title right there on the spot or would you go through the Elite 4 gauntlet again to make it back to the person who took your title. And regarding the champion you defeated to gain your title in the first place I take it they would be isolated in a dungeon like how Steven was in Emerald but they could still be challenged again except their team would be higher leveled that time around. But yeah it is a pretty interesting concept overall lol.
And agreed on Red's Pikachu. My Tyranitar at level 65 survived an Iron Tail and OHKO'ed with Earthquake lol.