My involvement with Vantage was solely during a long rail journey to Manchester VT wih Don Kershaw and Neil Pittaway, so Neil tells the story of the edit system that nearly was.

Vantage...pity we have no pictures but, basically, the reason for its development was that none of the commercial systems at the time allowed the unique BBC Editor ways of working, particularly with regard to sound. (for a period in the late 1980s we did examine all the current commercial offerings, using Edit Suite B on the 4th floor of the Spur as a test bed).
What we needed was a serial control editor that had the total flexibility of Electra with the additional variable speed capabilities required for new generation VTRs and would also allow assistant editor involvement if required. Designs Department built a prototype which was everything we asked for but it was becoming likely that, in the long term, the future of Designs Department, by then slimmed down to a non-manufacturing design group, was in question and support for Vantage unlikely to be sustained.
Sony's new 9000 editor was just becoming available and seemed to offer much of what we were asking for. (Not really surprising because we had been in dialogue with them). Sony provided us with a bespoke BBC version of the 9000 (the 9100) which gave us as near as possible a 'Vantage'.