Think maybe London to Paris with the Channel Tunnel Rail Link added as well, think that would be good.
I am sure many would like it. However to date TSW routes have not been very long and there have been discussions as to whether there are some limitations as to what can be supported in particular on consoles. London to Paris is around 300 miles multiples of what routes currently are on TSW. Although the idea of going through the tunnel sounds interesting I do wonder whether the 25 minutes or so in the tunnel simulation would be that exciting at least on repeated usage. My own experience in the real tunnel is that after the first trip through it looses its novelty pretty quickly. Others may have different experiences. Beyond the route length there would also need to be for accuracy a lot of track around St. Pancras, Gare du Nord and the tunnel portals themselves. So if anyone did take it on it’s not going to be a small task!
As much as I'd love to have the Eurotunnel and driving an Eurostar through it, the main, and biggest issue is licensing. There are some people in the community who know even more than me and they told me a few years ago that the problem is that Eurostar is not interested in a licensing deal and having their trains and liveries in the sim. In fact some people in the community still wonder how Eurostar hasn't taken down yet the freeware livery for the ICE 3 for TS2018. Another issue, and this was Matt who warned of us of it, is that beause over years people have made videos of TS2018 which include derailments and crashes in them, several companies have refused licensing deals because they don't want people to see that happen to rolling stock with their liveries on it and so they just don't allow DTG to officially include their liveries in the sim. So yes, companies are extremely picky with what they allow in the computer game as they want people to see the best possible image of them, overall the companies see this as marketing and if something even remotely bad is allowed in a game they strongly think it will damage their reputation and so they don't like it.