The i8 is not a track car, it was not intended for that. It will not do a track day - the battery will generate too much heat and shut down. Think limp mode.
I specifically asked this question of Jacob Harb, BMW i Brand Manager, when I met him in December at a private BMW i8 event at the SLS hotel in Miami.
He said "it'll do laps, but not sessions/days"
It is just not intended as a hardcore supercar.
Surely it will drive the canyons all day though - you're not going all out 10/10ths in the canyons. I will test this theory and report back when I get my i8.