I'm just wondering if anyone has made such a content port yet and if there's any issues? We'll shortly need to port in this manner so it would be nice if there's already some knowledge out there.
As Nuno mentioned, CP for Web 8 is not released yet. And CP 2013 SP1 officially doesn't support Web 8, so officially you can't use CP for that purpose yet.
But, indeed, for DXA 1.3 (which is also not released yet) we're using a 2013 SP1 CM Import/Export client to import in both 2013 SP1 and Web 8 without any issues. As a matter of fact, we even use the 2013 SP1 CM import/export client to export from SDL Web 8 to 2013 SP1.
I've not tried it, but there is nothing listed in the known SDL Web 8 issues: http://docs.sdl.com/LiveContent/content/en-US/SDL%20Web-v1/GUID-246EA11F-4CD1-4625-9FBB-5DE16C97A5B1
I've tried to import into Web 8 instance with the CP 2013 SP1 client but without any success.
First it (CP) displayed the error message: "one or more error occurs" after clicking further, it displayed the empty list of 'Dependency Type Group' and it crashed.
I was able to export content from Web 8 though.
I would wait until CP for Web 8 is officially released.