Services on the second tier seem to be getting strong interest. The DAPI is allowing all kinds of things that where impossible for a distributed system not long ago, traditionally centralised services running on a distributed platform.
Can you give some examples of what you think the DAPI will be used for? I'm sure there all kinds of uses that I can't even think of as this is brand new technology.
Payment processors are probably the most prime candidate for this type of functionality. Easily accessible payment verification will be a huge advantage for Dash in terms of ecommerce growth. I've come to think of Dash as being the "WWW" to Bitcoin's "TCP", take that as you will ;-)
To spatula, I think that with the DAPI, Dash can be a direct competitor to Paypal (easy of use, with login/password you can send money here and there), with less (or no) fee.