While it looks like just about everything they talked about isn't going to be in the game, I think challenge levels would have been an excellent idea. Or at least, challenge modes that, rather than changing the core game that they're determined not to change, just adding an extra element of replay-ability.
Based on the speedrun leaderboards in Stranger's Wrath HD, I'm going to guess they have something like that planned for N'n'T.
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