Any more on this, I would be keen to see it complete.. 
4th edition WHFB was probably building on the foundation of the already-published WFRP1e.
The WFRP1e core rulebook gives the present date as 2500 IC (p. 269), and says that the currently reigning emperor is 'Karl-Franz I' (p. 284).
The Enemy Within (1986) has a more detailed introduction to the Empire and timeline, and it says that Karl-Franz was elected to the throne in 2502 (p. 12), and though it doesn't give the current date, it seems to take the view that Karl-Franz is a young, inexperienced emperor. It does say that Karl-Franz is currently 35 years old (p. 14).
Later sources give us an approximate date of birth for Karl Franz. For instance,
Warhammer Armies: The Empire (2011; 8th edition) indicates that he was an infant in 2470 when he and his father were rescued by Wood Elves. If we assume that Karl Franz was born around 2469-2470, that would suggest that WFRP1e is set around 2504-2505. So perhaps we should take the '2500' in the core book as being a mere approximation.
In practice, for me, I tend to take something around 2515-2520 as 'the present', or as the best launching point for Warhammer Fantasy stories. From there you can easily launch into either the Storm of Chaos (canonically 2522) or the End Times (2522-2528), though most of the time I daresay you wouldn't want to.
