Activision Publishing CEO Eric Hirshberg, in an earnings call (via Gamespot), believes that Destiny will have a bustling long-term relationship with both DLC and expansions:
I think they're already co-existing. We had a full year of expansions to the game that have been very well received and sold quite well.
More recently, you've seen us introduce smaller, in-game purchases that allow people to customize their experience and express themselves; those have been very well-received and have sold well also. I think we've already shown that DLC and microtransactions can co-exist and that our community is hungry for more great content.
In early October, Destiny introduced microtransactions in the form of Silver for the purpose of purchasing taunts. It wouldn't be surprising to see Silver be expanded to other cosmetic items. I'm not fond of the slippery slope argument, but the fear is that we'll see less than, say, stellar uses for Silver in the future.
Hirshberg admitted that there are no "shifts in strategy" in terms of favoring microtransactions over expansions, but it did comment that they "have a lot of options at our disposal."