Interesting question. I don't know how many bulky silk yarns there are, but I went and read a bunch of reviews on Knitter's Review, just to see how silk behaves in blends. The general consensus is it has no elasticity at all and generally "blocks" to the same shape it was knitted. However, if you get wool in the mix, the wool is elastic and may need some blocking. Alpaca doesn't block either, so a blend that uses alpaca is going to be more difficult to shape. Also, some silk yarns are textured and splitty, but the more tightly spun yarns show gauge changes clearly. Lace hides that better than stockinette, but it's still something to consider.
I think it also depends on what you want the blanket for. I wanted a warm tv-watching blanket, so fluffy wool is absolutely perfect. It keeps me warm and the holes aren't an issue because the more solid parts of the blanket trap heat so effectively. I plan to use my blanket and not just display it. Some silk blends are much more fragile and susceptible to pilling. If you can't find a bulky blend, you'll use a fair amount of yarn and it could be expensive.
On the plus side for silk, it's shimmery and drapes and is luscious. Clara's reviews were so wonderful that I wanted to rush out and buy some silk yarns, but she never talked about a lace blanket on this scale, mostly due to the expense. Something like Jo Sharp Silkroad Aran would possibly be a good yarn to try, but even at Webs, it's $9 a ball and you'd need 7 or more balls to make a blanket.
If you try silk, I'd love to hear your opinions of it, especially for a project like this. I swoon over balls of silk yarn at my LYS but it's always so spendy. I have champagne tastes on a tap water budget.