Given that this game is essentially a lite version of IV, lots of stuff is still available in the game's archives, despite not being used (much):
Every character customization option remains intact (as per the Old Save Bonus, see below), except for the clothing and hair from Anime Pack DLC. That being said, there is only a dozen of available outfits to use - but the graphics for Image as Designed, Planet Zin and Rusty's Needle are still there.
Only half of the available outfits work properly on Gat and Kinzie's models. Gat's case is more interesting, though, in that, with some modding, you could dress him in his Super Homie duds.
Despite the game doesn't appear to have any radio stations at all, there is one, technically, with eleven metal and dubstep songs, which you could casually hear from bypassing cars. All of said songs appear to replace 89.0 Generation X.
Outside of stuff already available in IV, according to unused game code, Shakespeare was going to be a boss fight with multiple phases and the ability to grow in size and use his skull against you.
An update released shortly before the discontinuation of the online character design sharing features render the feature of having the customized Boss appearance from Saints Row IV unusable, and thus the Boss always appears as his default male appearance.
Troy Baker did not return to voice the boss, so Nolan North replaced him as Male Voice 1.
Role Reprise: Jay Mohr returns as Dane Vogel and Sasha Grey returns as Viola DeWynter.
Word of God: When streaming a preview for Gat Out Of Hell for Halloween, it was asked if the Zin were in Hell. The creators said they weren't, and that the Zin have their own afterlife.
