Vin Diesel says that a Groot movie isn't just something that he'd like to do, he thinks such a film will almost certainly happen eventually.
It's something that James Gunn has talked about and it's something that I know that he would love to do. Sure, I think it could be very interesting. I think it's inevitable, I think that character is so enigmatic. He was already one of the most unique characters in the Marvel universe, and I think what Marvel has done --- primarily what James Gunn has done --- to realize that character has exceeded beyond any of its expectations.
There aren't many different ways to interpret the word "inevitable." It seems that Vin Diesel truly believes that a Groot spinoff movie is something that will happen. Vin Diesel tells MTV that James Gunn has expressed interest in making the movie, which is the sort of thing that could get the movie made all by itself.Read more at Cinemablend