Looking at UK TS routes and bearing in mind some gaps are plugged by third party releases, if I was big boss man at DTG I'd do these. Updated Routes to 2018ish. Brighton to Victoria/Bedford. Great Eastern to now include Clacton/Southend/Sudbury branches & TfL branding/services. Great Western Paddington to Oxford/Bristol with Electric sections. Glasgow to Edinburgh Electric. WCML Preston - Glasgow New - Modern Edinburgh - Inverness Merseyside Metro Southern Coastway SWT Basingstoke - Weymouth extension to Portsmouth line. Trans-Pennine Northern (Manchester to Newcastle) C2C Crossrail New - Retro Kings Cross to York (1960s) London to Brighton (1950s - including the Brighton Belle) Varsity Line (1960s Oxford to Cambridge)
I hardly ever run modern routes, so I'll leave comment tol others. However, a freeware Kings Cross - York route is coming: http://forums.uktrainsim.com/viewtopic.php?f=365&t=150317&p=1849642#p1849642 which would also provide a home to various Pullman services. Instead of a 50s/60s East Coast route I would suggest the Waverley Route. To run the greatest variety of Southern steam (and electrics) a route centered on Guildford would be ideal. Part of the Varsity Line (between Oxford and Bicester) is included in the freeware route 'The Wycombe Railway and Joint Line', but I agree, the full route would be nice to have, although the Central Wales (also LNWR) would be welcome too. And then there is the Cambrian….
FYI there is ECML Echoes of Steam in the Workshop, it's a steam era version of the Newcastle-York route. For a steam era Southern network, SteamSoundsSupreme have Southampton-Weymouth including Castlemans corkscrew and it's free.
