True, and it's done. There are two very large DC lines in use:
The Pacific Intertie, from Washington State down to Califunny
A line from the Great Frozen North down to Minnesota.
IIUC, after the ice storm's enormous damage Hydro Quebec replaced their
interconnects with the rest of the grid (primarily New York and Ontario)
with a "DC buffer". Made it much easier for them to disconnect without
harm from the melt-down.