All the collections have had reduced items. Karl's stock was sold to staff for £1, Stella's had beaded jackets that got £100 taken off them, Victor & Rolf had pieces in sale for months... it happens. It doesn't mean it's unsuccessful. There will always be bits that don't sell.
Missoni would be amazing, but like someone mentioned before, Sonia Rykiel was knitwear. So I don't think a knitwear designer will follow a knitwear designer..
The menswear side of things is a bit sad. I do wish Stella had done a menswear range as well, I can imagine it would have been great. The Jimmy Choo men's bags were lovely, but sadly they only did the two pieces. Sadly menswear just isn't the focus for them, it doesn't sell anywhere near as much as the womenswear, so I think we'll always get a bit of the rawer deal out of these collaborations.