Let me make a case against the 'Schwenke' measure. The pedal points of mm.22-23, the F# moving to Ab, make an appoggiatura approach to the long pedal point on G. This effect would be broken if the 'Schwenke' measure introduced the G pedal point prematurely outlining it as a passing tone.
From the moment I opened the WTC vol. 1, one Question stood out the most: Why would Bach repeat each pattern twice in one measure? This may be a Baroque musical pattern? Why not extend the rhythm to one figure per measure? Or, perhaps it was meant to be slow and the repetition is to reinforce the harmony? This patterns also appears in Prelude No. 2. Surely that's not a coincidence! There is one exception to this rule in the second Prelude's measure 18, where the lower note changes in the second half of the measure.
By definition, a Prelude is a preamble. Like a closed book ready to be discovered, a prelude sets the scene for the unfurling of all the complexities of a fugue. The harmonies remain mostly diatonic and feature either triads or seventh chords up until measure 23. It is my observation that despite weaving most complex counterpoint, Bach is a master of outlining diatonic harmonies and uses chromaticism and added dissonance to underline form and climaxes. In measure 23, for the first time in Prelude 1, there are 5 different pitches in the harmony. Next time this occurs is in measure 28, and then measure 30, and in a very curious way in measure 34. In measure 34, we see Bach not just outlining a dominant harmony into a tonic, but presenting almost the entire CM scale with 6 pitches. Curiously, he omits the A, which is the highest pitch of the Prelude. The omission of the 6th scale degree also partially keeps the integrity of a dominant 7th chord resolving into the final tonic.