From what I've gathered both from the trailers and the open house:
The Open House showed both a chapter called "Timeline" after Retro and then the million project chapter, called "Million". This may indicate two new sets of songs, where million has 12 songs in total. Since only 10 are shown, there are 2 secret songs in the chapter. Timeline, on the other hand, only has 10 songs.
All of Million's songs are level 9 on hard difficulty. All of them. This most likely goes for the secret ones as well. Be Prepared.
Millions songs in order are:
Stardust sphere by Tsukasa (based on Total Sphere)
The Ricochet (not sure on this one, includes artwork from original story so might be based on one of the story songs)
The Sacred Story (based on Sacred)
Area 184 - Platinum mix by Persona (based on the original Area 184)
Gardenia by Yamajet (seems to be his new song)
Sweetness Overload by 3R2 and Dj Mashiro (based on the Sweetness and love, but expect this one to be freedom dive level people. Seriously. It's BPM is insane)
Les Parfums de Celebrez most likely also by naotyu (based on Les Parfume de L'amour)
Afterglow by Jioyi (Similar song and artwork as Future World by Killerblood)
Genesys by Kia (with the characters from the Knight chapter)
Storia by Xi vs Sakuzyo (Yes, Xi vs Sakuzyo. All Hype thrusters engaged)
The Timeline chapter also has new songs (information based entirely on Open House, so anyone who can understand what they are saying please correct me) This chapter seems to be based on songs from different time periods, as each song has a different time period when you scroll over it.
Penglai movement, level 8. Time Period: BC6,000,000 ( shows up as Penglaimovement when you first scroll over. May Change. I assume it is BC because of the chronological order of the songs)
Aboriginal, level 7. Time Period: BC8000
Dutch Formosa, level 9 Time Period: 1644
Empire of Japan level 5 (odd, would be first level 5 hard song after changes) Time Period: 1936
Money & Money level 7, Time Period: 1970
Phubbing level 8, Time Period: 2015 (song has a bar code, may need translating later on)
Protest level 9. Time Period 2057. (Protesting about nuclear development, links to next song)
Catastrophe level 8. Time Period 2059 (as title suggests, destruction)
Rebirth Level 6. Time Period: 2245
A New Home level 8 Time Period: Infinite
From the preview, it seems to follow a story of two characters throughout the whole of time as the world is created, destroyed and reborn again. It'll be interesting to see more information on this as its released.
Heres the link to the Open House recording (works as of 13/6/15) in case anyone wants to provide further info:https://livehouse.in/channel/rayark/record/-JrfoqtIV1eMTC2OwkmA