Yes, in a colloquial or informal setting, "X will be a thing" means that X will be popular, widely used, or widely recognized. I suspect that phrase might be used more in popular media than in reality.
Informally, "X is a thing" might also be used to mean that X will be a source of disagreement or contention or some sort of trouble, but this is probably even less widely used.
I agree that "It's going to be a big thing" is the clearest way to interpret this. I do run across "a thing" without any modifier quite often, but the way I most often see it is in the form of a question, particularly, "Is that a thing?" or "Is that still a thing?" which means "Is that event/trend/relationship/whatever still current or still going on?"
Hello, as you can see my native language is not English, so I just put the question exactly as was write (in the subtitle) and as it was spoken (I'm talking about some movie that I was watching)<<>>
Again sorry for my bad English, 'see ya'
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