@Digz - I've used trail runners in the berg a number of times... especially useful when you're undertaking a lightweight, speedy, long-distance traverse
However, if it snows, you will suffer... And I have sprained my ankle wearing trail runners in the berg before, so you need to concentrate on your foot placement a lot more.
My choice of whether to wear trail runners or boots comes down to season, daily distances planned and passes to be used. Trail runners on Icidi Pass would not be my idea of fun!