Is it beyond the wit of organisers to say that, in exceptional weather circumstances, tere will be flexibility in start times, and a maximum time that will be applied to all riders (15% more than 20th placed on the day), even non-starters on the day. Get the top 30 on GC going when the weather forecast is safest, thereafter teams fill the rest of the schedule in a similar "pick the order you like" to that used in a prologue. Anyone who is not GC relevant or fancying their chances of a stage result doesn't need to risk it, can just be given the maximum time.
Starting in reverse GC order maybe matters in a stage 20 or 21 TT, but not at stage 10.