Pixel artists will probably use nearest-neighbor scaling to display their art on high-resolution screens (so one pixel would become a sharp 3x3 block of pixels, or 4x4, 5x5, etc). That is already the technique being used to create games with an “old-school” aesthetic on modern gaming consoles.

I don’t think that drawing 1920x1080 (or larger!) images pixel-by-pixel will ever be practical, and it probably wouldn’t even look like pixel art to the eye at that point.