Already in 2015, Delta has added Aeroflot, Garuda Indonesia, Aerolineas Argentinas, China Eastern, China Southern, China Airlines, and GOL to the list of airlines bookable on delta.com with Delta SkyMiles. That means the following airlines' award space are now bookable on delta.com:

Delta
Aeroflot
AeroMexico
Air France
Alaska Airlines
Alitalia
China Airlines
China Eastern
China Southern
Garuda Indonesia
GOL
KLM
Korean
Virgin Atlantic
Virgin Australia

Not all Delta partners are bookable online though.