The McLaren MP4/4 with the driver pairing of Prost & Senna (alphabetical order) came close in 1988.
Only 3 races in to 2014 but the similarities are apparent, a totally dominant car with a stellar pair of drivers in Hamilton & Rosberg (again, alphabetical order).
So, can it be done, a clean sweep for the Mercedes team, winning every race on the calendar this year.
No one looks remotely close, if reliability can be preserved then ...............why not ?