I can hear your alarm bells ringing already.
The latest episode of Extra Credits covers the topic of Microtransactions. As I was listening to the rules of making a good microtransaction system, I was happily noting that DDO follows each of them... until they got to the part about cordoning off non-paying customers from paying ones. Which is exactly what's happening with adventure packs.
Now, I realize that the packs are probably the single largest source of income for Turbine (in the sense of TP spent on them vs other stuff). Lord knows they're the only thing I spend my points on. But, as the video points out, a good MT system is one that lets players try things out for free, and choose whether to pay for more of the same.
So, I'd suggest that every now and again, a couple packs would open up to everyone for a few days, with the special catch that players who don't own a pack can't get favor from its quests (to avoid TP farming). I can't think of a way that this could hurt Turbine financially, but I'm willing to bet that it'd drive up the sale of TP/subscriptions as people decide they want to own the content they got to try.