To put it simply, it will happen if the Ecuadorian government decides that it can happen.
If Quito were to grant permits for marine iguanas, or flightless cormorants, or what have you, to be legally exported, it would be possible for zoos to import. Marine iguanas are CITES II, which means that as long as an export permit would be issued, no CITES import permit would be required to bring them into the US. Right now, Ecuador has shown zero inclination to do so, but if there's one thing that should be evident, governments (and their priorities and willingness to stick with established customs) can be highly changeable.
It's similar to the San Diego Zoo Safari Park with the platypuses. The species was considered "impossible" to get because Australia wouldn't export any. Then, Canberra changed its mind (in part driven by a close working relationship with San Diego Zoo Global and Australian conservationists), and then they were allowed to import some