You've all been waiting patiently, and it's high time you got something in return. The Alpha Demo will showcase entirely the whole Midgar chapter, before allowing you to play through the remainder of Disc One with the new Rebirth spells, materia and limits breaks.
This release will come as a PPF for the PSOne NTSC ISOs. Using PPF-o-matic, you'll be able to patch your ISOs then either play via emulator, or burn and play on original PSOne hardware. Full instructions and a Rebirth Manual will be provided.
It's going to be good Christmas!