It doesn't make sense and wouldn't for a while. I don't think the potential would justify the market overlap, the work surrounding an acquisition of that size, and the risk of pissing off other large partners that Pinterest needs right now. Pinterest is still in the very early stages of monetizing and I'd imagine they want to get the current stuff right first.
Geeze. Didn't realize they'd hit 11B in valuation, though we don't talk about them as often as AirBnB and Uber.
I guess the question then becomes does Pinterest see it as being worthwhile to buy Etsy out or do they just run them out of the market? Etsy shop owners could simply "pin" links to their stuff and voila off we go. It'll probably come down to the cut Pinterest takes from the sales. If they offer a lower % than Etsy, they'll stand a chance at running Etsy out of the market and seeing a higher conversion rate.