An apparent member of Dovetail Games staff has said in post on Reddit that internally they are not targeting having the Unreal Engine version of Train Simulator ready in late 2015. Under the name 'Whiterider1' they added that it is possible though if most things are finished on time or early. They also said that Dovetail Games are likely to include backwards compatibility with older versions of Railworks and that one of the main things they were working on is getting the software to able to run on more PCs through optimization hopefully meaning that it will finally include multi-core processor support. Despite this I would still say that backwards that backwards compatibility (while more likely) still seems unlikely with it most likely being sold as separate software through Steam.
As well as this 'Whiterider1' answered many more questions including one about a Channel Tunnel route by saying that they are no plans to make one as 20 minutes of it would be in a tunnel pointing out that people complained about how much of London To Faversham was in tunnels, and hinted at more steam routes coming in the future as well as much more you can read for yourself at: http://www.reddit.com/r/nerdcubed/comments/2iav61/nerd%C2%B3_plays_train_simulator_2015/
This person was confirmed by the moderators of the "Nerdcubed" subreddit as being from Dovetail Games other than that I have no other evidence.
For your rail and bus simulator news check back on RailSimulationUK.blogspot.com.#
UPDATE: 2014/10/07: The posts appear to have been removed but can probably still be found cached somewhere.
