Not really talking about Ravenloft at all (its just the distraction caused by the ENWorld article that got me thinking), but rather what are things that are expected/sacrosanct and what are things that might be tried.
Ah, fair enough -- so the real question is, what's too much of a sacred cow not to be changed?
Ideally, nothing. If the campaign doesn't take risks and try different things, it's just going to get stale and be more of the same-old same-old after a while. This may be a good thing for the folks who haven't yet gotten involved (for which it's all new regardless), but at some point you're going to get an exodus of existing players who are tired of doing the same old thing over and over again.
Since Chris Perkins likes to use Blizzard as an example, we can talk about World of Warcraft -- how many folks are former WoW players? That wasn't such a big deal when there were still plenty of people who hadn't tried it, and thus old players getting bored with the game could be easily replaced, but the marginal cost of replacing those players gets higher all the time, to the point where WoW, despite still being one of, if not the the biggest MMO out there, isn't anywhere near where it was when it appeared it would be the giant game that would last forever.
Given that AL has very little budget to allocate toward that rising marginal cost of attracting new players, I think the campaign is best advised to keep the existing game fresh so that current players are less likely to leave from boredom, as well as recommend the game to others to keep the fresh players coming in.
That's my $0.02US. Of course, you may know all that and are more looking for specific examples of what kinds of things to try. Might I recommend a Ravenloft season? ; )
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Pauper