I'm using the 'Extract Assets' feature in Photoshop CC 2014 but I'm running into a problem where I am not able to select any file type besides PNG-32 from the File Format dialog dropdown. Any ideas why this might be?
This appears to be a bug in the application which has been reported here.
(I am the Product Manager responsible for this feature, so I would love to be able to fix it in the next release!)
That's certainly curious. I just tried it with a vector smart object as you have in your image and I was able to add different formats quite easily:
It might be worth reporting this to Adobe as a potential bug with this new dialog.