Stepping away form the GM metrics thing today due to a topic that came up on twitter and demanded more than 140 characters.
The idea of a collectable RPG has been with us pretty much since the initial success of Magic: the Gathering. The idea of producing an RPG with a similar sales model - collectable elements, variable rarity, repeat sales - has always held an appeal, but has never really materialized. This is probably just as well, since I'm not sure the CCG model holds up well for RPGs, but the model is not the idea.
Lately, I've been starting to see collectability show up in RPGs from an entirely different angle, and it's kind of intriguing. I trace it back to Fiasco, which is not itself collectable, but which created the model that allowed it. Fiasco uses "playsets" as part of its model, and while the book comes with a number of playsets (and the forthcoming Fiasco Companion will have more) there have been many more playsets released on the internet. As rules material, these are more truly "modules" than published adventures which use the same term. They an be seamlessly swapped in and out, added or removed, all without changing the game.
When Apocalypse World came out, it followed a similar model with its "playbooks," each of which was basically a character class. As with playbooks, the core book came with several, more were released, and they could be seamlessly swapped in and out. Simple enough, except for one simple change: friction.
Playbooks and playsets tend to be pdfs, which means that distribution is easy - all it takes is someone putting them up for public consumption. The AW playbooks were never distributed that way. There is no central reference for them, nor place you can download them. They've been distributed under distinct circumstances (such as parts of promotional bundle) and, unless you actively follow the game online, it's hard to even know these are out there.
But they're not just thrown down a black hole. Instead, the expectation is that they will be freely swapped and shared from person to person. The files are still easily moved around, but the lack of central reference means that their distribution needs to be at least somewhat personal. That is to say, they're collectable, traded and swapped in a manner more reminiscent of bootleg tapes than CCGs.
This is an interesting model, and its strengths and weaknesses both tie to how well it pays off for the fan. Once a fan knows about these things, he needs to dig around to find out more (which is rewarding in and of itself), get his hands on one or more of them (rewarding for cachet) then share them (rewarding for being able to help). In short, there's a huge emotional payout for putting in the work (and, of course, keeping the game in mind). Certainly, some will be alienated by this - it takes time and effort to engage in this kind of viral marketing - but in a fashion similar to ARGs, the enthusiasm of those who buy in tends to offset any losses.
Obviously, there are some community-building benefits to this, but the biggest advantage is one of pure marketing. Forced scarcity is a classic way to increase demand, and this is a great example of it. I've been a believer in the commercial advantages of the "rules module" approach in general, but the introduction of scarcity & collectability is really the sharp end of really canny marketing.
A big part of what makes it work is that it needs to be paid for with effort and interest, not cash. Cash is nice, but invested effort guarantees future buyers, which means more cash. It also means you avoid backlash. For comparison, look at WOTC's cards for Gamma World and other products. The cards themselves follow the CCG model (where some are rarer and more powerful) but WOTC has been bending over backwards to NOT market them in that fashion. And for good reason - the idea of being able to buy a more powerful character doesn't sit well with most folks. Collectable rules modules get around this in two ways - first, they don't offer more power, just more options, but second (and perhaps more critically) they don't require money, they require investment. If there's a playbook you want and you don't have, you can get it, you just have to want it enough to hunt it down and initiate a trade (or make a request).
Which is to say, you can't really complain about it, because if you care enough to complain, why haven't you just used that effort to get the module?
I underscore that this is brilliant marketing. Consider: it's not going to be to everyone's taste. Everything I've listed as a benefit is going to be off putting to someone, but that very alienation is an essential element to making those who have invested feel like they're more on the inside. If we were dealing with just money, this would have nowhere near as potent an effect, but we're paying with things that carry much more weight (effort & investment) so it's a force multiplier.
Anyway, I expect to see more of this in the future. Even if it's not used to market a game, it's a great way to keep a fan base engaged, so there's a lot of advantage for a company that has a game that can support this and a willingness to put in the work. Hell, if anything, I expect to start seeing more interesting developments in the metagame that this kind of trading represents.
I would be remiss if I did not mention a game in the pipeline with some of these ideas in mind, Guestbook, a project from David Hill which is also doing something interestingly experimental on kickstarter.