How do the sandals attach? Extra webbing/stitching/buckles/lashing points could easily offset the weight savings of the lighter fabric. I would crunch the numbers if I were you.

And keep in mind that the sandals will constantly be abrading that fabric. Maybe they'll be wet and gritty. If there's any part of my pack that I don't want to have fail, it's the bottom.
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If you only travel on sunny days you will never reach your destination.*

* May not apply at certain latitudes in Canada and elsewhere.