The article is behind a firewall, but here is a link if you have a subscription to WSJ:
https://www.wsj.com/lifestyle/travel...hp_featst_pos5

So, the new planes are apparently approved and flying! My take away from the article:

"It’s the luck of the draw for now. Southwest, mindful of its already chronic preboarding issues, has no plans to announce the presence of one of the planes at the gate. And there won’t be any sign it’s an extra-legroom seat until later this summer when a different color headrest is added.

Keep your eyes peeled. “Your odds are low in May,” Southwest operating chief Andrew Watterson says. “Your odds are high in October.”"