I would honestly like to see something unique and original done with the DDR unlock system... while some of the ideas I have might not be original, they would be original if done in DDR and wouldnt necessarily be the exact same.
Has anyone honestly thought of looking at Pop'n music as an example of how to unlock songs in a music game [and I am not talking about the crappy slot machine on Pop'n 10, thats Konami's worst ever attempt at any unlock system] I have noticed that each CS release of Pop'n has had unique and original ways of unlocking the game depending not on the players skill mostly but by little mini games which are fun to play and completely random usually in what is unlocked... this gives the player more freedom and fun in unlocking stuff since they dont have to be a hardcore popper or even an intermediate popper to unlock the content.
As for good unlock systems in Pop'n that could be used in DDR... Pop'n Tourist was pretty fun in Pop'n 11 but was nothing more than an enhanced version of play til you unlock it, Sugoroku de 8 was a good unlock system in Pop'n 8, The theme park construction was a fun system in Pop'n 13, and the best unlock system which I think could be good for a game like DDR would be Gambler Z from Pop'n Music 9
I would love to see DDR have a quest mode like unlock system similar to Gambler Z in Pop'n Music 9... while Gambler Z took forever to unlock, it was interesting in the fact it was a randomly generated dungeon with treasure chests hidden with song unlocks, extra mods, hidden characters, additional items, and coins which were all random aside from the Boss Charatcers you fought at the end of the dungeon. The Bosses were ridiculously hard if not impossible and whether or not you could pass them eventually you will win the battle after 3 attempts... Imagine something like Pluto Relinquish, Fascination Maxx, or other Boss songs being at the end of the dungeon on Oni The unlock system was done by moving your character through the dungeon by the number of steps... also you could roll the dice depending on the number of stages cleared. In DDR you could have the standard 2 dice for a complete game and if you get the extra stage you could get the third dice to go with the multiplier.
Think of this... You could pick a DDR character [Emi, Rage, BabyLon, Yuni, Alice, Ruby, Gus, etc] and they would be your dancer moving their way from place to place on this gameboard type of setting. So after you clear a set of 3 songs with or without extra you then play the minigame and roll the 2 dice and then the multiplier dice... then your dancer moves the amount of spaces needed to progress towards the boss. Whatever treasure you pass such as song unlocks, hidden extras, and other things is all randomly generated meaning one player might have some songs that another player doesnt have yet... I think the randomness of Pop'n 9 made the game so much more fun to unlock since you never knew what was going to be unlocked or if you were even going to get an unlock after that round... so your dancer moves their way around the DDR town or space or nightclub or wherever they move through unlocking stuff along the way. You eventually meet up with a Boss along the way and have a challenging boss song to try and beat them at [you get the 3 attempts to beat it then it auto unlocks and you auto win] and Bosses can be past characters like Devil Zukin, Naoki, 2mb, Paranoia [that robot in the back of Paranoia songs], and that guy giving chase in the background to Maximizer. Ultimately after all 5 bosses are cleared all the boss songs are unlocked and all the treasure will eventuallly be found and you will have a full unlocked game.
And it doesnt have to be a randomly generated dungeon like Pop'n but maybe since its DDR it could be a large mega sized maze with different directions in which the goal is to find the 5 bosses [since the last few DDR games 5 was the magic number for Boss songs] and defeat them. The fun part is that the unlock system isnt a normal mode... it would be played at the end of any regular DDR play you make in game mode or nonstop... just like Pop'n it would be a quick mini game at the end of each round where you roll the dice and watch your character move the number of steps rolled unlocking whatever they can along the way if anything since I have gone about 3 full rounds of Pop'n 9 before even unlocking anything at times.
Or another idea would be using the similar Gambler Z mini game but instead dressing it up a little bit and replacing Toru Kamikaze with Robo-Zukin and calling it Zukin Wars... The goal would be to lead your robo zukin through the randomly generated maze finding treasure and defeating the bosses at the end of the maze in which there are 5 bosses and a hidden boss after the 5 are defeated... you could even have the other Zukins from previous DDR games make an appearance in the mini game like Oshare Zukin, Maid Zukin, Kaeru Zukin, Princess Zukin, and Dark Robo-Zukin then bring back Devil Zukin by making her the ultimate hidden 6th boss thus defeating her, fully unlocking the game and winning the Zukin War!
Sorry but it was just a brainstorm... I would love to see a Pop'n music 9 type of unlock system utilized into a DDR game... the possibilities of what can be done to DDR to not only enhance the Story of the DDR characters but also use it as a means of an unlock system is amazing. That and it would cater to players of all skill levels since Beginners could play the mini game and start unlocking the features, advanced players can unlock stuff and its nothing more than a large board game of unlocking by rolling the dice and moving across the board. And since everything but the Boss songs is randomly generated unlocks can be fun since each player will have different things unlocked also adding to the mystery of what songs are unlocks.