A 1031 exchange is applicable to investment property. A residence is not eligible.
Moving out of the house gives him some flexibility to declare his current house an investment property, and if his next house is his retirement house, then deferring the capital gains tax can make sense even if the cap gains rate increases later. The rules are complicated and can be time consuming (especially for converting a rental property into a residence), but if you have a large chunk of equity in a house (in some areas of the country, having $2M of equity is not unheard of), and are already planning on being away for an extended period anyway, it may be worth it.
In any case, if he has a lot of equity in the house, taking to a tax or financial advisor makes sense.