George L. Glaser's Auto Letter from Europe column in the August 1, 1960 issue of Automotive News has some interesting information about the then yet-to-be-announced VW 1500.
In the first item in the left column he reports that "the larger VW model, with a still larger engine and modern styling, definitely will not be introduced before the Frankfort [sic] Auto Show in September, 1961, informal sources say." Glaser's shadowy "informal sources" seem to have had their facts in order. This is the earliest mention I've found of the "big" VW in the automotive press.
The other interesting thing about his column is the Frua-bodied VW 1200 pictured at the top right. Known both as the Italsuisse Volkswagen and the Volkswagen Sun Valley, this coachbuilt special got a lot of attention when it was unveiled. There was even a plan to put it into limited production, and a Porsche dealer in Florida was ready to act as the distributor in the USA, but VW refused to supply the necessary chassis to Frua. It's understandable that VW wouldn't have been very enthusiastic about aiding the development of a car that would be in competition with the upcoming VW 1500, not to mention the fact that, although they were affiliated for a time in the late '50s, by 1960 Frua and Ghia were at odds. Frua's relationship with Ghia soured while they were working in collaboration on the designs of the Renault Floride/Caravelle and the Volvo P1800. Cutthroat politics behind the scenes in Turin. More information on the Italsuisse VW can be found on this site devoted to the work of Pietro Frua.
In the caption Glaser reports that "with VW coming out with a larger model, probably in 1961, there is speculation that the newcomer may be influenced by the styling of this body." What he didn't know is that the designs of both the VW 1500 sedan and VW 1500 Karmann-Ghia had already been finalized by late 1959 and were already in the prototype stage by 1960. Considering the close yet contentious relationship between Ghia and Frua in those years it's even possible that the VW 1500 Karmann-Ghia was an influence on Frua's design rather than the other way around.