According to KGI analyst Ming-Chi Kuo, the limitations surrounding the MacBook Pro’s support for greater than 16GB of RAM will be lifted this year. Apple is expected to adopt Kaby Lake processors (months after the PC community quickly embraced them), and at the same time offer a 32GB RAM option.

This will likely be a build-to-order option

Source: Hot Hardware – Apple’s 2017 MacBook Pro Refresh To Bring Kaby Lake And 32GB RAM Option