Season passes are not new, nor are the idea of expansions. The former has been present for a number of years, while the latter had been around for almost 15 years worth of gaming, especially in the PC space. The Witcher 3, and its parent company CD Projekt, have strong roots in the PC space. With this in mind they have adopted an approach somewhere in between the season pass and the expansion.
The aptly named expansion pass will include a handful of larger content chunks than most season pass users are used to, but also the company has committed to releasing free downloadable content as well. Following the launch of the game the company released 15 pieces of free downloadable content ranging from costumes and minor additions all the way to the release of new game + for free. The company has always maintained a strong relationship with its fans and always, tends, to look out for their best interests.