Why not normal Marik? He's already in the game files so it could be possible. The quote suggests that it's Arkana next, but the non-Yami version of Marik will probably make it into the game too at some point. Maybe in an event like Yugi Muto and Mokuba.
I feel like "the duelist everyone has been waiting for!" Implies that it will be Marik, nobody here is waiting for Arkana.. Dont get me wrong he would be nice, but hes definitely not the "one we've been waiting for".. Hopefully im right, tired of waiting for Marik.
The duelist everyone's been waiting for is definitely Yami Marik. Arkana is going to be the one that comes before YM in mid-July. The Arkana-event will be the one that leads to the YM-event at the end of July (even though I still think it would work better with normal Marik event leading to Yami Marik, but the quote is from Arkana, so it's probably him mid-July).
If Marik's ever going to be an obtainable character, then I'd be the hap-hap-happiest person in the world.
Hopefully he and Yugi (and Mokuba) will really be unlockable sooner or later (better sooner than later)