Yes, Byword for iOS is here and it looks good. I just bought it and it's downloading on my iPad as I write this.
I used and loved Byword on Mac for about a year, until iA Writer, which I've used on my iPad, released their iPhone app and added iCloud sync. The convenience of iCloud convinced me to switch and it's been great.
Now that both Byword and iA Writer have Mac, iPad and iPhone versions with iCloud, I'm going to use both to see which one I like best. They're both awesome, so it'll be a tough choice.