Quick thoughts

My immediate mental reflex to the suggestion of piccolo in Après-mystère is:

1. The character of the opening fits the suggestion admirably.
2. I had already written the canon so the flute and clarinet should stay out of one another's registral space . . . the greater expansion of the range with the substitution of the picc. may make the whole passage a bit more dramatic.
3. The only thing I perceive as a possible 'loss' as a result, is the unison on the last note.

However, if all else proves musically satisfactory, I can recast that final unison an octave higher, making a slight adjustment to the clarinet line leading to it.

So, we may find that an alternate version of the piece for piccolo is born.