If 2D comes back, it will probably be due to people yearning for the colorful art of anime and the warmth of old Disney cartoons. Stuff like that feels inviting to get lost in, especially as a lot of it was based in how to draw people into the story and have them feel wonder.
Realistically, I think there has to be a draw back towards traditional animation again. But it can't just be 'Traditional is better then CGI' it has to be 'What can we do to make traditional look magic again?' and 'What should inspire people about it to want to use it as a medium?'
Traditional is not as big here anymore unlike, say, places in Japan, because we've mostly quit showing anything anymore with it. We mostly now rely on trends on what kids 'want' so we can sell toys and use that as an excuse to not try anymore to be creative. This naturally limits what people can do as far as risk taking and creativity, and it's also always seemingly CGI now, because CGI often is the only offered or proposed profitable option in a lot of cases.
However, it's not a forgone conclusion that 2D is down for good. Often older stuff gets revived because it's ostensibly better replacement is ultimately found wanting after the novelty has worn off, or wasn't as superior as was once thought. Amazon uses cassette tapes to hold massive amounts of data, the Air Force is on their umpteenth F-15 after trying with the F-22, and some of of the best selling videogames are sprite-based or have that old retro style. 2D could have this same kind of renaissance, but it's going to take a while. People are still infatuated with the newness and possibilities of 3D, it's faults are mostly going to be overlooked or not acknowledged right now because we're still in the 'honeymoon' phase.
