I don't see any reason for it not to be open in December, the exterior looks to be fully done - the delay is probably in renovating the inside (I was in Kiev recently)
Looks like it's gonna be a nice property, brand new. The location is really quite good, 5-10 minute walk to Kreschatik, the main drag in Kiev. Closer to downtown than the Radisson SAS (about a 5-10 minute walk from the Hyatt)