For those interested, Microsoft will be releasing Killer Instinct Definitive Edition for Xbox One on September 20, 2016. The retail package (a disc - YES!), contains all of the content of seasons 1 - 3 as well as Killer Instinct Classic 1 & 2, an original soundtrack and a gold Gargos skin which is exclusive to this package. There are also some obligatory extras like trailers, character art, etc.
The entire package will retail for $39.99 which is a nice price to get all 26 characters, 20 stages and two classic games.