It pretty much has to be Meachum. I don't want to drag in the whole "casting an Asian-American actor" debate, but let's assume, as seems likely, that they go the whole blonde hair, blue eyed route with Danny. A lot of his villains are steeped in Oriental-ism and Asian imagery which makes sense as they tend to tie back to Kun-Lun, but if you use them as your main threat you are essentially saying, "Okay, making the main character an Asian martial artist is racist so instead we'll cast Asians as the ancient, wise martial artist mentor, the nameless ninjas he'll fight, and the kung-fu bad guy and that's all fine so long as the hero is still a white dude." I have just enough faith in Marvel to believe that someone, somewhere along the line would stop and point out how absolutely terrible that would be.
I'm not saying that those villains aren't usable and can't be fully developed, compelling characters that go beyond just being a yellow peril stereotype but I just highly doubt that they want to start the show off by presenting the story like, "So here is a white kid who goes to Asia, wins one of their warrior titles, then spends the rest of the show beating up evil Asians." It would actually come off even worse since this show will be on the heels of Luke Cage, a series that is sure to deal with racial issues.
Meachum not only makes sense as a reason why Danny would be brought to New York, he just presents less problems than other possible antagonists. Use the others, fine, maybe start to set up Davos because, yeah, he can be a great part of the Iron Fist story. But mostly stick with making Meachum and business interests the main conflict.