Can you make whipped cream with a SodaStream?
No, because the bottle would explode off the Soda Stream, spraying cream and foam all over your kitchen.

Per the Soda Stream FAQ:


  No. Only water should be carbonated in the SodaStream Sparkling Water Maker. You risk damaging your Sparkling Water Maker, not to mention making a big fizzy mess! The money-back guarantee and the warranty are both invalidated if you carbonate any liquid other than water in your Sparkling Water Maker. Stick with plain, cold water and adding any one of our fantastic flavors - AFTER the water has been carbonated! 


Speaking from personal experience, the Soda Stream won't tolerate anything even a little more viscous than water ... not even fruit juice.  The liquid foams too fast and blows the bottle off the device.  Cream would be a hilarious mess.