Re: Dwayne Johnson is Like Cage?
The Rock and Chris Hemsworth are both 6'4" tall - so there's nothing to worry about in terms of one dwarfing the other because they're both big dudes.
With that said, I wouldn't mind seeing The Rock portraying Luke Cage in the MCU. The only problem is that I don't see where he fits into the storylines they seem to be going with into Phase 3. It's pretty apparent that they're going the cosmic route for Avengers 2 and by introducing Ant-Man & Doctor Strange afterwards I'm not sure a Heroes For Hire movie makes a ton of sense.
While I think Luke Cage & Iron Fist would make a great pairing for a feature film, I don't see the characters coming to life on the big screen any time soon - it's more likely that they'd show up on the Agents of SHIELD show at this point, but knows for sure?