I think BMW has enlarged the mini line as far as it can go and still be recognizable as a mini. I have to wonder if sales for the countryman and clubman are less than expected.
Is Saab a good fit for BMW remains to be seen. But let's look at it from the other side. As one person said already this is the best possible scenario for Saab.
The other bidders consist of companies in newly developed nations China/India/Turkey that want a way into western markets. Building a brand takes a long time and Saab although slightly tarnished still has good brand recognition. There is some precedent that this combination can work, geely/volvo, proton/lotus, tata/jag/land rover etc..
Still I believe BMW has the best chance to get Saab up and running in the shortest amount of time. BMW has experience reviving a dead brand like mini. I also agree that they hope to compete with VW in the mid-range mainstream market.