While the first 747s were designed as passenger aircraft, the design was always provisioned for the freighter version (which was the main driver for the upper deck flight deck).
A primary reason for that was, at the time the original 747 was being developed, SSTs were also being developed and were expected to be in common service by the mid 1970s. The thinking was that the SSTs would quickly make subsonic aircraft obsolete for long distance passenger service - so the 747 was designed to be readily converted to a freighter.
Of course we all know how that turned out
