The TGV Sud-Est was the first TGV to be built back in 1981. These served on the LGV routes between Paris, Lyon, and Marsille from the day that they opened, up until 2019. Shortly before the opening of the LGV Méditerranée, the TGV sets that had been assigned to the route had their top speeds upgraded from 270kph to 300kph. The other sets, which kept the original top speed of 270kph were used on TGV Lyria services until their replacement with the TGV POS in 2013. Images from Wikipedia
If one were to make the TGV Sud-Est, I would no doubt recommend making the time period to its first few years, including the Sud-Est trainsets in the original orange paint scheme. It probably best captures the 80s aesthetic out of anything I've ever seen from the decade in rail. Here are some videos showing of what operations would look like. Set number 16 setting the record of 380km/h (236 mph) on February 26, 1981. Plus I don't know if I'm the only one, but I do get tired of all these present day set routes. One of the reasons I love train simulation is to be able to experience years past somewhat, and not just watch footage or a small train navigating a loop. But there is one consideration, the distance of Paris to Lyon is 264 miles, meaning that it would be impossible to make such a long route, thus, one would have to have a cutoff point in the middle, particularly taking advantage of the high speed portions. However I don't have quite a good understanding of the network, so I don't know whether it'd be better to originate in Paris or Lyon.
I've already looked into the idea of doing a Paris to Lyon route and I agree that doing the full run from Paris to Lyon would be too long for a single release, although possibly doable for an exteded route. Looking at the route, the best way to do the Paris - Lyon route would work best if broken into Paris - Creusot & Montbard, and Creusot - Lyon. Additional routes for Montbard - Dijon and Dijon - Lyon could be added later to add the route between Paris and Lyon via Dijon. Splitting the line like this means that the line can be modelled in 140 mile chunks that can be stitched together, similar to some of the routes already in game. Despite the desire for a 1980s setting, I feel that a modern version of the route would be better, so that it can be stitched together with the current TGV routes to give players the full Paris - Marseille line. Then again, I don't think that much changed along the route between Paris and Lyon between the late 1980s and the late 2010s.
