Mid December is traditionally the date when European rail operators make significant revisions to their timetables, and 2015 is no exception. The most significant change in the Balkan region is a welcome one: after a gap of several years, there will once again be a daytime service between Belgrade, Niš, and Sofia. The existing overnight service continues, so travellers will have a better choice of departure times. The daytime train (named "Balkan") leaves at 07.35 from Belgrade and 11.30 from Sofia, and the trip takes around 9 hours.
It seems that this train will carry at least one Russian Railways sleeper car from Moscow, probably with extensions to the Black Sea and Adriatic coasts in summer. This is by no means the first time it has been possible to travel directly from Moscow to Serbia, Bulgaria, and Montenegro, but there had been a break in service due to the withdrawal of many services that passed through Ukraine. These sleeper cars will now take a more northerly route via Minsk, Warsaw, and Budapest.
There are few other major changes affecting Southeast Europe. The "Serdica" Budapest-Sofia service introduced last year will continue to operate but with a completely different timetable. It will now leave Budapest in the early morning and Sofia late at night, so the part of the journey through Bulgaria (and probably the crossing of the Danube) will be covered in darkness in both directions. There is also a significant timetable change to the "Citadella" from Budapest to Ljubljana, which now leaves in the morning rather than at lunchtime, allowing a late afternoon arrival in Ljubljana.