In my elaborate ending scenario - which I wrote out the details of somewhere on this board before we had this thread - Dean doesn't make it to the Grand Canyon, but he experiences it in heaven (because in my scenario they go to heaven.) This happens, because in my scenario, after Dean dies fighting some epic battle with Sam, Sam continues on for a little while, but not only to continue hunting for a bit, but to make sure to do the things he knew Dean wanted to do - go to the Grand Canyon, go to the Netherlands, maybe even go to Yemen (because it's funny, and entirely Sam's humor) - so that when he also dies and connects back with Dean in heaven they can experience it together through Sam's memories.
I imagined the final scene happening something like this:
Sam follows the road in heaven and finds Dean in the field of fireworks. They reconnect and after a moment, hug. There would be a brief conversation about how Sam ended up there with Dean finally saying:
Dean: Well, we have forever. Eventually I'm gonna get bored. Have 'ta cause some trouble. Not yet though. I wanna enjoy this. We earned that.
Sam: Sounds good.
Dean: What should we do first?
Sam: How about The Netherlands?
Dean: We never made it to the Netherlands, remember.
Sam: But I did. I even made sure to go to your coffee shops without coffee. Or there's the Grand Canyon, a beach in the Cayman Islands, fishing in Costa Rica. We'll do it all.
Dean: That's ...awesome.
Sam: I know. I'm an awesome brother. Dean gives him a look. Where to first?
Dean: How about an amazing diner I know first to get some awesome pie? Or maybe New Orleans for some beignets. I've got places to take you, too. But we should probably start slow, not burn through 'em all at once.
Sam: Good plan. But, don't worry. We've got a lot of choices.
And as they walk towards the Impala to go down the road. Dean can be heard saying "I think you're gonna like New Orleans, Sammy." And Sam replies, with a wry smile "Yeah? Well, wait 'til you see Yemen."
A movie or limited series would come from when they got bored. I'd love for them to band together with Ash and Charlie and Bobby and cause problems in heaven. There could be a spin off sort of where Ash, Bobby, Charlie, and ooh, Rufus would help reconnect souls that have been separated and generally cause trouble up in heaven, and Sam and Dean could help out once in a while.