It seems Tilted Mill have come under the wing of Vivendi/Sierra, who own the rights to make Caesar games, and that is how it is possible to make this new game. Not unlike the arrangement between Vivendi and Blizzard North that produced the Diablo series.
The site says they will retain the elements that made CaesarIII the huge success it was. They are doing away with walker access and going with something similar to what COTN uses. I hope they don't blow it here. The game will not work if it's a case of sitting for very long periods waiting for things to happen. Player input is the key to the playability of C3.
One element from C3 that I really hope they emulate is its famously low system requirements. I don't expect to be able to play C4 on a Pentium 120 but I would hope that it will run on a machine of 1,000mhz with any of the commonly available graphics cards. COTN was a bit of a worry in this regard, especially as your city grew larger. My machine (1150mhz, 512mb RAM, g-force 4) will not run COTN properly, even though it ran the demo sort of OK.