I am currently helping my company migrate to 2013. We are seriously considering using the Oslo theme given the look and feel but not having the global navigation is a big downer. I've attempted to locate the code in the master page to turn it back on and even went so far as to copy the global navigation code from Seattle. While this makes it visible, the drop down navigation doesn't work and the styles can't be updated. Any suggestions on how I can make global navigation visible and functional?
Here is a guy who makes a comparison about the 2 templates
The quick launch (current navigation) has been a part of SP for a long time and it is useful most of the times.
You can do the reverse and remove the quick launch with an easy code in pages where this is needed.
Since you want the Oslo layout with global navigation. Have you consider using Seattle master page and remove the current navigation zone entirely?