It would be fully awesome if we find out that Rickon/Osha being gone all that time meant they were hiding in the North, plotting. Robb proved his mettle, especially with the Umbers. I'd love to see a total mind fuck where Rickon gets brought back to Winterfell to do the slow conversion back to the King in the North.
But I agree the easiest explanation is probably the correct one. Rickon is likely just there so Jon can save him and then restore him to his seat. Sansa will probably go the way of the books, (seems to be hinting Petyr coming back into her story) and with Arya and Bran having their own shit going on, Rickon is the only heir.
That wolf head looked super small - I'm trying to reread book 1 now, but from what I remember, Shaggy was a freakin monster, and super wild. I sort of feel he'd be the hardest wolf to take down.
Fully satisfied seeing that asshole Ollie get his though, god damn. Worth the price of admission right there.