Despite the votes on this question (and answers so far), I don't believe anyone has actually answered the question:
Which begs the question, what would a sus4 chord mean if you were playing the whole tone scale, or perhaps the blues scale?
First, we have to understand what a suspension is:
Suspensions have three parts:
- Preparation - introduces a non-chord tone
- Suspension - sustains that non-chord tone (often through a harmonic change)
- Resolution - resolves the non-chord tone to a chord tone (almost always downward by step)
In the example, we begin with an Em6/4 (second-inversion), but on beat 4 the E moves to F, a note that does not fit in an E minor triad. The new note is sustained through a harmonic change (it still does not fit into this new chord), and then finally resolves downward by step to a chord tone. In this case, it happens to be a C major triad.
So, back to the question, What would a sus4 chord mean if you were playing the whole tone scale, or perhaps the blues scale?
Well, using suspension predicate the idea of tension and release. You create tension by moving from a chord tone to a non-chord tone, changing the chord, and then bringing it back.
Blues is a predominately tonal musical genre, and like most genres, is not rigid. Midnight Waltz by Cedar Walton, is a 24-bar blues in 3/4 that makes extensive use of suspensions. In this context, suspensions (4-3 suspension) is used as an Upper Neighbor Tone that prolongs the larger harmonic regions forward, creating a sense of movement:
In music that uses whole-tone elements, you would need to handle it differently. The whole tone scale is by its own invention and purpose, non-functional, harmonically speaking. Suspensions, as we have established, serve a harmonic function. So, in order to use a harmonic-functioning device in a predominately non-functional context, you would have to manufacture the impression of harmonic function. Otherwise, the effect is meaningless. The answer to that question, is for another time.
So, to summarize, as another stack user said quite succinctly:
"An argument can be made that any sus chord that satisfies these theoretical elements is valid. In the blues context, both a half step above the third and a whole step above the third could theoretically achieve this. Midnight Waltz provides an example where a whole step is used. Other examples probably exist where a half step is used." - jdjazz