One of the biggest draws of these Adventure Paths is that they give everything a GM needs to run a long-term campaign with little preparation on their part. They normally start with a beginning party, dealing with a straightforward low-level situation, and let things expand and escalate until the group is dealing with something large-scale, maybe even world-changing.
The original APs, "Shackled City", "Age of Worms", and "Savage Tide", were all twelve-part stories published in Dragon Magazine (while it was still bring printed). All of them gradually increased in scope, and included references to classic D&D material. For instance, a late adventure in the "Age of Worms" path required the party to fight an undead dragon first mentioned in the map for "White Plume Mountain", one of the first D&D adventures.
These campaigns were written to take a 1st-level party and take them all the way to 20th level or higher. (The D&D and Pathfinder rules have a soft 'cap' at that level, but include optional rules for going beyond that.)
A proper adventure path for SW would have to start with something simple, but gradually expand to include traveling halfway across the world, and maybe even a little plane-hopping (though I don't think anyone would willingly travel to the Pales). The end would have to involve a face-off with one of the many Ancient Evils, of which there is no shortage.
It would certainly be a daunting task to write one of these. But I must agree with the others -- I think this is something that had been missing from Rolemaster all these years, a long-term scenario that gives GMs everything they need in one package.