Apparently I didn't word that section very well, because many people took away this impression. My apologies. Factorio will continue to support X11 for as long

Apparently I didn't word that section very well, because many people took away this impression. My apologies. Factorio will continue to support X11 for as long as SDL does, in other words, essentially forever. The only change here is that X11 is no longer required for the game to launch at all. SDL will load whichever video driver is available at runtime, or if you have both, you can choose which one to use in the graphics settings.