Suburu doesn't support flat towing starting in 2016. Note that the car was not physically changed, but they will not honor the warranty should there be an issue. Sounds like they pulled support due to a liability issue and not a mechanical one.
There are a couple of threads on this in the toad section. I seem to recall one person bought a 2016 to flat tow and Suburu gave him a refund due to the flat tow issue. I am seriously considering the Crosstrek, but will likely go used with a 2015 if I do.
2005 Newmar Kountry Star 3742 - Gas
ACME Eze Tow Dolly
2008 Chevy Malibu Toad