As I understand it, SegWit and increased blocksizes are two completely separate issues. SegWit improves efficiency, and is the equivalent of a 2Mb blocksize, or better. It introduces a number of other possibilities as well. As there is no immediate need for a blocksize increase, it would be better to implement SegWit, and then see what is needed for the future. Who knows, maybe the Litecoin and Bitcoin chains should be combined to facilitate exchanges.