Since I last posted here, this map has been started again from scratch. I've been working on it more recently and hope to find the time to make a video introduction to the map soon. I doubt it will be a series (mainly because I imagine far fewer people are interested in this than in the GB map), but one or two videos will hopefully follow. Here are some screenshots for now.
The map is now larger than it used to be (owing to a more detailed scale) -- 5700x5000 -- and covers the highlighted area below:

The nostalgic among you may remember that this is almost exactly the same area covered by the 'Orient Express' scenario in Railroad Tycoon 3.
This map is not like the GB map, in that I am not trying to simluate the real-life rail network of this area, but rather to reimagine it in a world where (a) political boundaries matter less, and (b) these countries have a level of rail investment closer to that of Western European nations. Nevertheless, all services fully timetabled using convoy spacing, in the same way as the GB map -- the difference is the timetables are entirely fictional.
Here's a screenshot of the network map, showing progress on the newest version of the map:

The cluster in the middle is Budapest. Vienna and Bratislava are in the north west, while the cluster at the south is Belgrade. The furthest east point so far is Baia Mare in western Romania -- so, as you can see from the Google map, I've really only made inroads into about a third of the map's area so far.
Here's a screenshot of Subotica, a busy junction in northern Serbia:

The main line from Budapest to Belgrade passes through Subotica, a city of around 140,000 people (IRL). What's more, several local and inter-regional services terminate here, making it a popular transfer station. To the west, trains travel via Sombor to Osijek, just over the Croatian border. To the east, services travel to Arad in Romania via Szeged in Hungary. Finally, an hourly service from Subotica to Timişoara, also in Romania, travels south along the mainline for a short while before branching off via Kikinda.
I am currently finishing off the lines in Slovakia, after which I will pay attention to the tiny parts of Austria and Czech Republic in the far northwest of the map.