Honestly, after reading Marcel interview all four parts for Racedepartment you can get pretty good idea, there is a lot mentioned, perhaps enough for five years.
If judging on how much has been released out for us in the past year, I don't expect great amounts of improvements even in five years. But decent amount of new content, which will actually be less important if software will not keep up. But if most work was underground on UI, Competition system, The Grand Tour game.... then perhaps good leap could be expected after it is out and out of developers tasks list.
In the upcoming five years I also expect hardware to evolve, so average PC will be much more capable, and developers will be able to unleash more, so almost certain improvements because of that IMO. Of course nice optimisations for software itself will be performed, which will have similar effect, such as a loading times decrease which should roll out in days to come. I think ray tracing will start picking up momentum in the industry, and it very well could solve of some most annoying rF2 graphical disadvantages, such as shadows and reflections.
Big big hopes for online activity to jump up. As much as I have had an opportunity to have little bit of rF2 online racing, nothing could beat it.
So yeah if it would be managed to make multiplayer very alive and well functioning, then it would be literally new era for rF2. Hopefully thats closer than years, and more likely months away.
Modding should increase if modding tools for blender gets introduced, and there is a comfortable modding flow to be found. It will never be like AC, because rF2 simply does more stuff, so content has to do more stuff as well and the quality standard will keep getting higher, those things will limit amount of mods.
Content from S397 will be probably pretty steady how it is now. No road cars. Perhaps one or two classsic car per year, maybe none (depends if rF2 needs more players, or only modern race cars fans are enough). A lot more GT3 and GTE cars. Hypercar class will proove to be awesome, so there will be those. For tracks there will be big names, when all endurance tracks gets collected, there will be tracks that are raced by the GT3 and GTE cars naturally, there will be some less known tracks, that will be awesome to race too. There won't be classic tracks released.
Community will grow exponentially, till it will reach ~3k daily players in the best case scenario. Worst case - will remain like it is this day.
You will see less and less logical and mechanical thinking from community, as cars are all very modern and more electronic and aerodynamic than mechanical. The simulation might not increase a lot, because less knowledged community will build up a critical mass (a lot will come from AC and ACC) and there will simple be not that much demand for more realism, even possibly the opposite. Other titles might catch up rF2 physics feel, though probably none will reach the level what rF2 can do.
Rain will get improved a little, but not much. Because too few people will like the idea that sometimes it rains IRL, and that it can be incredibly tricky at some times.
Temperatures will finally work in rF2.
AI issues will get addressed, and it will get better, but complaining will remain forever.
Transmissions will get improved, but not so much difference for Hshifters, as the released cars and general simracing trands will result in it being almost never used anymore at official servers. I mean there will be almost only modern GT cars. Forget Skippy, forget Vee, forget 60s F1, new simracers will not know very well what does it mean to have only mechanical grip.
Sound will be improved a lot, once rF2 gets pretty neat everywhere else, and then naturally sound will start to be really really annoying, like as Senna said "some people thinks they have big problems, because those are the only ones they have"
