Hi Ted,
The asynchronous playing directly results from the polyrhythms, which is one of the hallmarks of late romantic music. They all used it including--Scriabin, Liadov, Rachmaninoff, Bortkiewicz, Glazunov, Catoire, etc. That's not to say that Brahms, Chopin, Liszt or Schumann never used them, they often did so. But beyond their era, the polyrhythms seem to become even more pervasive in late romanticism. At least that's the way I sense it.
Regarding the penultimate chord (actually two of them), what I did was to play the preceding five dissonant chords very quietly. Then for the penultimate chord, I voiced the top note, a D# in the right hand and the bottom note, a B in the left hand. Aurally it gives the sense of an interval of a third which I think sounds quite nice in the coda. I also made the second sounding of the chord even more quiet. Finally the soft contra B in the left hand reaffirms the tonic key of the piece and brings it to a close.
This prelude is one of Scriabin's best in my opinion. I'm delighted that you enjoyed it so much.
Thanks, Ted, for listening and commenting on it.
David