Bach lets the harpsichord break out of its usual supporting role and take over the musical argument? That gives the passage a freedom and momentum that can sound closer to later Romantic virtuosity than to a typical Baroque concerto.
@Bumbles Exactly so. Plus no-one knows in what fashion he played the music either. It's my favourite moment in the Brandenburg Concertos which some people again down play by claiming that it's all very much tendious repetition
