I wouldn't be surprised if Marik was only in the data for cutscene purposes and possibly events, similar to, say, Strings or possessed Joey. (Umbra & Lumis are likely in the same boat, and will probably just be used for a Battle City repeat, given they "appeared" in the event anyway.)
No clue what they'll use Solomon for, if anything.
(cont.) There is definitely a lot more hope for Kalin and Bruno since they are on the list. Atticus is on the GX leak list, but once again, I can't find any images. Then there is Jaden/Yubel and Zane again. But simply being on the leak list doesn't make them unlockable. Awhile ago, Para and Dox were listed separately and that was the tag duel. The other Jaden and Zane could be event only.
The only thing that makes me think Marik might still be real was the images of him on the character select screen, icons, and even a duel loss image. I don't know if they were planning to do it at first, but then looked at his cards and said "WTH were we thinking?"