Is it possible to change the image size of the thumbnails in the new media uploader?
For example images are currently displayed using the "thumbnail" image crop size and I would like them to be the "medium" image crop size.
Supposing that I'm interpreting your Question correctly...
The thumbnails displayed in the new Media Uploader are already the
So, it's a matter of applying some CSS styling to increase their size. Maybe other style adjustments are necessary, this is just a proof of concept.
change max width and height to the size you want