The challenge that DAFs pose to NGOs is important because it represents the same challenge posed by small - which is to say most - foundations. The challenge is that these resources are effectively hidden from the nonprofits view. Often deliberately.
According to planned giving research, donors - now more than ever - have foundations AND DAFs AND checkbooks - and nonprofits need to learn how to navigate these options when approaching them. Recognize that if you "walk" through the door to a small foundation, the board members have other resources in other places that might also be deployed. Tides and community foundations have typically helped the donors "manage" these options - and I use the term manage loosely, and only to convey the fact that these intermediaries have 'sold' these options to donors, not helped donors make sense of each or the whole.
Much more needs to be done, for both donors and nonprofits, to make sense of these "giving portfolios." Donors need to think about why they have each tool and how they complement each other. Nonprofits need to learn how to ask about each one, find access, and make a case that fits each pool of resources (or some of them). And vendors - e.g. Tides, community foundations, financial firms - need to help donors know what to use when and why.