The devs don't really tend to do sedans anymore - the last one we've gotten (that wasn't a body style of another car, like the 800 or Nine) was the Bastion, and that was released almost four years ago. And considering we already have three low-end FF midsize sedans (and the Wendover was changed to a coupe to avoid a fourth FF sedan being added), I'm not sure if the devs will bother with adding another one any time soon. Especially when we have three post-2000 sedans in the game (800, Bastion, Sunburst), one of which is FF.
none of the modern sedans in-game are reasonably comparable to, say, a nissan altima. that's why i included that niche
It's the same reason they haven't bothered with a modern D series yet. What's the point? It's just another pickup at the end of the day, then people are gonna complain that the old D series has 2000 configs and the new one only has 500. So they do all that work for....what exactly? The new pessima is the same as an Altima, cause, again, what's the difference? A slightly different body, a nicer interior? The devs have said they try to fill a niche, or a void in the vehicle library. I'll say it again and again: a bespoke race car/open wheeler is something worth doing. GT3 versions of cars are something like 80% different. They could make GT3 ETK K, SBR, Scintilla, and they can be stand-alone cars. But spending valuable time and resources to make basically the same car twice, from the ground up, shouldn't be a priority right now
I wonder how much ground you could feasibly cover with an 80s sports prototype. There's Group C1/JSPC D, Group C2/JSPC C, IMSA GTP, IMSA WSC, a road car retooled for GT1... Going back further, although it wouldn't be as versatile, a 70s prototype (Group 5 1970-75, Group 6 1966-82, Group 7 1966-75/Can-Am, etc.) could be simpler to engineer.