Also: Thanks David for the interesting article!
My thoughts:
When I raised a post regarding 'fluff' fiction for a theoretical new edition and book, I had people who were dismissive of the very idea. I thought that was interesting, because I was coming at it from a "new people coming in" perspective. I was interested that some of the forumgoers here were not supportive of an 'onboarding' system.
Narrativist: Ars 5th (the only one I particularly care about) isn't really narrativist - its mutliple systems through all of its game books simulate the lives of various magicians and other things. IMHO games like WOD or Scion aren't narrativist either, they are just systems that understand their modelled stories bypass their rules systems on multiple occasions.
That being said, I personally believe a narrativist system is one which controls the 'flow' of the game, more like FATE, FUDGE or BURNING WHEEL. Ars has story flaws, but the application of the resolution of those is done through simulationist means.
Scaffolding: I'm going to pull out this one - I'm an intelligent guy and I didn't get ARS until Kidgloves who had played previous editions ran a game and ran us through the rule system. I'd run multiple game systems of varying complexity previously but I could not begin ARS because it was basically incomprehensible to me. I find this is a problem - I imagine that after Ars 5th won its award, lots of people (like me) bought it. And failed to play it. And failed to buy any expansions. This isn't a super cool business model.
My suggestion for onboarding/scaffolding: I would avoid moving toward a narrative system completely, but I would agree a free PDF for an intro to the game (NOT Calebais) and its various rules and systems would be super useful for getting into the game.
Another simulationist game I've recently got into is very impressive - It's just as old and twice as annoyingly complex for minor rules in some other book somewhere - Battletech. They explain openly in the beginning of their books how their modelling takes place and I would suggest that for some mythical 6th ed (or a new 5th ed product) could benefit from the ideas. Both Battletech and White Wolf use these prodigiously... and WW is successful and BT is regaining popularity.
I don't think whether a game is simulationist has much to do with whether it is popular. I say that the onboarding and scaffolding of the systems have far more to do with that than anything.
Their idea: Art, Fiction, Introductory Rules, Full rules.
What does this do?
ART: It gives a particularly evocative image in the minds of new people for what battletech 'is'. White Wolf follows this intensly. Desperate people in frightening artwork. Battletech has powerful looking mechs with giant guns striding over and owning the countryside.
Fiction: While I was dismissed by some people on the boards here, Battletech uses this as an integral part of their system for getting people in. They have decent writers (I don't say great writers, but decent) showing pilots of battlemechs and other things that demonstrate key parts of the setting. High lords politicking. Mechwarriors fighting honorably or dishonorably. The poor little people who get stomped on.
White Wolf are one of the most successful companies today - and not because their system is any good. It's broken, doesn't do what it wants itself to do, has deliberate limits on the system to prevent exploitation - and then is easily exploitable anyway. It's just not a great sytem. Why are they so very popular? Because they focus on the story. They present the story in short (fairly mediocre) fluff text, and have fluff fiction littered through their work. White Wolf are one of the biggest sellers out their, rivalling D+D if not outselling.
Both BT and WW have multiple published books in their setting which are likely from fans. The fans (and newbies) buy the books, see the adverts inside the books and this is yet another scaffolded step onto buying the game itself.
Introductory Rules: Battletech does this in full colour with a sample mission as a part of their (very worthwhile) Introductory Box Set. White Wolf had those little sample adventures they put off for free. Both act as an easy step into the real thing. I assume that WW actually made the sample missions to be played... but I suspect they acted more as teasers for people who would then go out and buy their core books. Both of these are glossy, colourful, and interesting to look at as well as functional and playable.
Full Rules: WW is easy to get a grasp on, BT is.. not 
. But in both of these cases they have scaffolded, produced high quality and interesting stuff to look at, and are both relatively successful in their fields.
If Ars, the niche simulationist game that it is, employed these methods - then it doesn't really matter if the system is complex. The system is robust, far better than WW systems. It rewards great stories and it rewards campaign, long term play. It's only real failure is that short term play isn't rewarded overmuch. I can only imagine that if Ars did some of these marketing tricks that it would achieve more sales - and get more newbie Ars players in rather than them just drifting along to D+D or WW like most newbies do. I know that these things take a fair chunk of money, though .
...
I got excited there, sorry