There are all kinds of theatres that call themselves 4D or 5D. Smells, moving chairs, mist, fans, temperature stuff... There is no standardized definition for it.

What I'm trying to say is smells in cinemas are really niche because consumers don't demand it. Consumers don't demand it so hardware manufacturers barely make smell sensors. Hardware manufacturers barely make these electronics so AI won't use these electronics.

This is news to me, are there really movie theaters that inject smells into the theater? And is that what they're calling 4D movies? Or is that something else entirely?

AI Can See & Hear, Will It Ever Touch, Taste, or Smell?

IMO your question is identical to if 4D or 5D movies will ever take off. They're a flop and will never be mainstream. Cinemas that have have smells are just rare quirky gimmicks. 

The reason why I think these are the same topic is that as long as our hardware doesn't support these sensors, neither will AI ever use these sensors.