I don't see this so much as a merging of the 1D lines, but as a tombstone of the 1Ds (primarily because of the name jump to 1DX).
And now that this is pretty much official, this is how I see the future Canon lineup:
1DX: FF 18MP, top AF, top FPS, Dual DIGIC V+ Single DIGIC 4
5D3: FF 32MP, decent 45pt AF, 4.5FPS, Dual DIGIC V
6D: FF 18MP, same(-ish) sensor as 1DX, same(-ish) AF as 5D3, same FPS as 5D3, Single DIGIC V
7D2: APS-C Maybe a slight MP bump, slight AF bump, 8-10FPS, Dual DIGIC V