What's next after the Sierras/Rockies/Colorado Plateau?

How about the Mt. Robson area of Banff N.P. in Alberta – the North Boundary trail and/or the Moose River trails would meet most of your criteria. While the Berg Lake trail is busy, the rest of that area is much less used and dramatically scenic.

@ RVP I think you can point the BPL search feature specifically at your subcategories and find answers to your question. There have been many trip postings here about Scotland and Scandinavia (Manfred Kopisch for example).

You might need to alter your notion of wildness. In reference to Scotland, while there might not be paved roads you are often moving across terrain that has in the past been impacted by humans. Also the weather can change much more quickly, and while there might be stone shelters with roofs every 10 miles or so there is no marked path.  Unlike the Sierra Nevada, however, you can plan to visit the occasional single malt distillery.

Alaska. You can do bush plane fly in trips where you can go as long as you want without seeing another person and hundreds and hundreds of miles without a road crossing. It is true wilderness. The same can be said for much of northern Canada.

South Island of New Zealand

Thanks for the suggestions everyone!  I have searched BPL for routes Norway, Iceland, Scotland, Canadian Rockies.

I identified several great routes, but they are primarily on trail — I could not find any “Sierra High Route”-type routes for the above locales.

I’d be curious if there are good off trail “high routes” that people have identified, particularly in the Canadian Rockies.

Perhaps some alternates or parts of the Great Divide Trail (Canadian Rockies)?