We have reproduced some of our map documents in ArcGIS Pro. When I export a map to EMF from ArcMap, the typical file size is around 300 KB. However, when I export the same map from ArcGIS Pro, the typical file size increases to around 25,000 KB (the example map in the image below resulted in a 298 KB EMF from ArcMap vs a 25,481 KB EMF from ArcGIS Pro, with the same export settings).
I have tried adjusting the resolution and image quality settings, but have not been able to solve the problem this way. These settings can cause the file size to vary, but only a very small amount. I have also tested the issue, making sure that there are no transparent or rasterising features in the ArcMap map document and the ArcGIS Pro page layout. I double checked this with the "detect rasterisation" script here http://arcg.is/2qp6pb2
We are very keen to move some of our workflows to ArcGIS Pro, because many of ArcGIS Pro's new features are advantageous to us. So far, this issue is the one thing holding us back from proceeding. Any suggestions very welcome.
I noticed Sarah had a similar issue, but with PDF exports here.