IGN has an interview with Geoff Johns about his episode of "Smallville" guest-starring the Legion. It's part of a much longer interview, and the Legion stuff (Smallville and otherwise) appears on the last page.
Asked about that episode, Johns said, "I'm actually in Vancouver all week for the filming. Wait until you see it. So far it's been amazing to be involved with the writers in Los Angeles, particularly Darren Swimmer. And the cast and crew have been awesome – Tom [Welling], Allison [Mack] and Kristin [Kreuk] are in my episode and they are freaking amazing. Tom came up with a fantastic addition to the Legion Code, he impresses the hell out of me. He keeps the energy up on the set, keeps things fun, and he's unbelievably smart. He approaches everything with incredible intelligence."
... Johns went on to add, "I love who they have playing the Legion. They look great. I'll talk more about them when they're announced. But they freaking rock. Legion rings, the villain's weapon -- holy s**t, wait until you see HIM-- "Grife!", they are the Legion."
... "I've never enjoyed myself this much on a set, ever. Watching everyone work so hard to bring the Legion to life is a dream. But the superhero of the show for me has been the director, Glen Winter. I'm amazed to watch him, how instinctual he is on the set, how much he's embraced the Legion, how he directs the actors and his shot choices…
... Asked if he had to make any tough compromises to make the Legion fit in the Smallville world, John replied, "I'm actually surprised by how faithful the Legionnaires will be to the comics. It's really faithful to the comic book series. Who they are as people, what they do, it's all in there. Obviously it's going to be a little different because they're just coming back for the first time to meet Clark. They're uniforms are the Smallville versions, not spandex. But I'm really happy with how faithful it is. And writing the first live action of the Legion is an honor."
Elsewhere in the interview, there's this:
IGN Comics: With the current Legion book coming to end with issue #50, it looks like Legion of Three Worlds might be the last huge Legion story we see for a while. Is this your attempt to close the book on all three of these Legions?
Johns: I don't know if you can say that. It's definitely not the last Legion story, just the last story of this era. There will never be a last Legion story.
I do hope I get to write the Legion again soon. I have a lot of ideas.