The Giro d'Italia has been to Israel and was supposed to go to Hungary last year. The Vuelta a Espana has been to Belgium and the Netherlands. It is not just countries next to the host country that can have these races.
Also, I hope you can get enough nominations to get this quiz featured. I see we both have made 100+ quizzes with 12,000+ takes but with no feature yet. I think this might be the one for you!
I think San Marino may get a pass-through in 2024 when the Tour starts in Emilia-Romagna. The 2025 Grand Depart is in the Netherlands, so it will pass through some combo of Belgium, Luxembourg, and Germany (if not all). I could see Portugal, Slovenia, Norway, and Sweden being on the list as well. Slovenia is a cycling-mad country, with some of the biggest stars in the peloton being from Slovenia, and the atmosphere would be like it was when it started in Denmark.
I think they would need a couple rest days to get back to France. It would also be cool to start in French Polynesia. I'm sure a lot of people would like to visit Tahiti. Logistics might be a bit challenging, though.