Back in 2014 it was decided that large-scale LEGO® exclusive sets would all be released under the Ultimate Collectors Series banner. This meant that playsets type sets such as the Death Star, Sandcrawler, Ewok Village and Assault on Hoth would be treated in the same way as traditional UCS sets like the Y-Wing, Slave 1 and the ultimate USC set – the Millennium Falcon. This caused a little be if a outcry from certain LEGO fans who didn’t agree that playsets should be treated in the same way as display vehicles. But it seems there has been a change of heart, with the reveal of set 75222: Betrayal at Cloud City, the Master Builders Series has been introduced. The Master Builders Series will comprise of bigger playsets, where as display-type ships and vehicle will continue to be released under the Ultimate Collectors Series banner.
The LEGO Group has provided a statement:
The Master Builder Series models are large playsets and beside being complex builds they are characterized by having many play features and functions, interior details as well as a range of minifigures. Ultimate Collectors series will remain highly detailed display models providing complex builds with a focus on authenticity and both Ultimate Collectors Series and Master Builder Series will continue as a way to highlight the unique characteristic of each style of model.