I doubt a direct to DVD movie would have the budget to hire any of the main actors from the previous 4 installments as well as the much more sophisticated visual effects. I expect that if they were to make a new movie then they would use Weta digital (the company responsible for the effects of the Lord of the Rings movies) for the CGI of the Chipmunks like they did with Road Chip since they did get a slight re-design. Not only that, the budget for Road Chip was $90 million, most of which for a movie like this goes into the reCGI; and since Road Chip made the least amount of money of the 4 instalments, that's why I doubt we'll ever see a 5th one.  

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