(17 gsm is 0.50 oz/sq yd according to my sums.)
Need to be able to SEAL the windward end against spindrift, but this applies equally to breathable nylon.
Certainly would need to pay more attention to ventilation in the field - but to be honest I can't see that as a problem.
Mind you, the 70 g you save is not a real lot for all that expense and hassle. Real problem is, as someone said recently, the inner tent is not that big a fraction of the whole bundle.