I am lazy. The clothes I wear the most are those that fit me well AND can be worn straight out of the washer and dryer. If this jacket had any chance of being worn more than once, it had to withstand that treatment. And so the fabric had to go through it as well... The upholstery fabric samples were squares 68cm on each side. They aren't that anymore. Now they are rectangles, 64cm wide by 57cm high! This is a lot of shrinkage, but it is not the end of the world because there is still enough fabric for the jacket. I don't even have to change the layout of the various fabric patterns.
Even after some careful ironing (which in retrospect obviously did more against the shrinking than the fabric's hand...) the fabric will never be its old stiff self.
I've thought a lot about what to do and I decided to go on anyway. The fabric is not completely limp; as you can see in the photo there is still some body left. Plus, since I have to use a different fabric for facings anyway, I've chosen a stiffer cotton duck. I definitely checked, and the duck doesn't loose its stiff hand after a wash and dry cycle. I'll use this duck as an underlining, giving the fabric more body. That will take care of the problem.
I hope these are not famous last words... wish me luck!
Ah, yes, another small detail. I made the original muslin in size 16, but I got the feeling that it was too big, and not just as part of the off-the-body design. So I made a size 14 muslin and indeed it fits better while still retaining the intended shape. No other modifications were necessary, so tonight I'll start cutting into the upholstery fabric.