Since they compared it to the Horus Heresy my hope is that the game will be based of the current (AoS 3.0/4.0? by the time this is released?) AoS ruleset just like the Heresy was built from 6th edition 40k, warscrolls may exist in a similar format to how they are in AoS and all that will change are added layers to the games core rules that allow for larger battles. The model line should hopefully be the same scale as AoS just like HH range can work in 40k armies, I think they'd shoot themselves in the foot otherwise.
Rules wise I think it'll be its own game with units not being compatible with AoS but the minis themselves will be. Then again 4 years ago I thought it would be stupid to move armies all onto round bases and look how that turned out lol.