I had my heart set on either Aronofsky or Cronenbourg directing but I think this is perfect Gondry territory going on Eternal Sunshine and The Sciene Of Sleep. The project needs an ambitious, courageous, quirky and visual director and I think Gondry is the main man.
I'm going to say it now and predict:
Mark Ruffalo as Joe Chip and Gondry's ubiqitous character actor, Tom Wilkinson, as Glen Runciter. I'd like to see Gainsbourg and comedian David Cross in supporting roles. What's great about this book is that there are plenty of laugh out loud moments even though the main themes are very spiritual.
Inception proved that metaphysics can breed blockbusters. Let's wish Gondry and producer Steve Zaillian (Schindler's List, Gangs Of New York) the best of luck.