Just discovered Framer Studio supports retina images (2x) out of the box. I'm so happy about this!
When I export UI assets from Sketch at 2x as PNG and drag drop it into Framer, it works, width/height will be in 1x and everything nice and sharp on a retina display. So far so good. But manually positioning elements is going to suck.
So I tried importing the exported 2x assets into Sketch again on a 1x artboard. For the assets I setup an export setting of the groups at 2x PNG and when I used Framer Sketch import, everything works like a charm! I didn't know this was possible.
By the way I'm doing this for a web app prototype. Not sure if this applies to native mobile apps. Would love to work in 1x though also with mobile apps. Sorry for the long post. :)