Brighton - LBG/ VIC would be fantastic. It was to me and many others a staple in TS, would love to see it re-built for TSW, With an Electostar 377 / Class 700 with potentially a 387 thrown in, 377/ 387 pretty much same bodyshell and sounds with some minor tweaking on lights / Windows / interior view. and the 700 gives a great Desiro soundbase. Have spent many many hours on the BML and would love to fire this up in TSW, especially once Third Party dev's are allowed to add on to TSW there could be similar to what has happened with route joining with the BML, MML, and SLN, Which has provided me and i'd hazard a guess that it has aso provided the community with thousands of hours of enjoyment, and the Workshop joining of the route actually gave me the final push for the MML so if when opened up there is a possibility for the Dev's it makes a great addon sales target!
Only if goes from both London's Victoria station and London Bridge station to Brighton (basically the existing London to Brighton and South London Network combined at minimum) then I think it's a good idea.