[fulafel]

To the first question: Yes. See eg https://en.wikipedia.org/wiki/List_of_HVDC_projects

It's not as attractive for managing nuclear accident risk as you might think, as nuclear is already struggling with cost competitivenss even without HVDC lines, and risk reduction per buck of other safety design features are better.

But it's brilliant for eg hydro (for obvious reasons), wind power (because 2000 km away it'll be windy when you have local lulls and vice versa) and solar (2 time zones worth of distance balance out production/consumption peaks nicely).