Again, you're overestimating these people. They're not paying attention to that kind of thing. They watch for swords, blood, bewbs, and cock jokes.
It is stated plainly, several times, that "we have Rickon Stark, the heir to Winterfell."
My wife, who watches maybe every-other episode, knew the significance of Rickon coming from out of nowhere.
In most cases, I'd agree that shownlies aren't clued in enough. But this was stated plainly for them. If they listen the dialogue at all, they know.
And again... it's useless to criticize the showrunners for making Rickon inconsequential... that comes directly from GRRM himself. Criticize him, if you want to criticize Rickon's demise. His demise is made inconsequential by the fact that GRRM played a giant joke on everyone with Rickon's character (much the way he's played a joke on everyone with all of the Direwolves, basically).
But the show never communicated how important he is. They threw out the Grand Northern Conspiracy and The North Remembers and all of that.
Yes it did! It told us that Rickon is the rightful heir to Winterfell. You don't need the Grand Northern Conspiracy to know that. Unless GRRM totally changes Rickon's fate (which I have a hard time seeing, all things considered), the Grand Northern Conspiracy will somehow fail, anyway.
Rather than political intrigue about the rightful heir to Winterfell, we get Jon Snow rallying a grand total of two(?) houses to his cause against a relatively unified northern army fortified in Winterfell. His claim that "battles have been won against worse odds" is horseshit. They never should have / would have launched that attack. But obviously we got Littlefinger ex machina because apparently his ability to teleport around Westeros is transitive to the army of the Vale.
I agree that it sucks that we don't get all of the intrigue, but the show doesn't have the luxury of hundreds of pages to beef things up. That's also on GRRM, not the dudes running the show.
And Jon is going to face terrible odds, no matter what, even in the books. Littlefinger's dealings in the Vale with the Old Guard have to be the setup for what we witnessed in the show, right? It's just gonna be setup and go down a bit differently.