I know that the MIGMET1 variable (metro of residence 1 year ago) stopped being included in data sets after 2011, presumably due to the boundary changes. Will it be coming back once there are five years of new-boundary data (the 2016 and 2012-2016 data sets)?
You are right that there is no reason that this variable can’t be updated. The IPUMS USA team is planning on updating this variable with the release of the 2016 ACS samples. In the meantime you should be able to update this variable youself by creating a crosswalk with MET2013 and PUMA. Then you’ll be able to identify the metropolitan area of residence 1 year ago by using MIGPUMA1. Note that, as with pre-2012 samples of MIGMET1, metropolitan areas are only identified if the size of the metropolitan areas was large enough to be identified by name under the confidentiality requirements.