The currently-in-work update isn't only about rebuilding track surroundings and object details, but it is a requirement to refresh all definitions of materials and textures to work correctly with the new lighting model.
With the new lighting model you get not only more track detail, but also time-of-day graphical effects which is important for the 24h races being a possibility in the future.
I hope we can agree endurance races with sun-movement is more than just a "track detail" (IMO it's substantial part of the gameplay experience with endurance racing, even if it would "just" graphical effect and nothing more). The current patch is of course only one step toward that, so it may feel like "meh, just details", but without this step there wouldn't be the following ones.
BTW, with regards to modding... so after this new shader/lighting system will be released, guess what would happen to all the mod-content out there, if the LFS would allow modding. Yep, it would render in wrong colours/lighting and generally talking it would be broken and each piece would need fixes from the community.
I don't think that would be accepted very well either (I don't want to guess what is worse, if not allowing modding, or breaking all mods at the same time with new version, I have no idea, I just don't see any fully-happy scenario except "release tomorrow new version with new content, shaders, physics, modding tools, curated leagues, etc..." and that's obviously not going to happen).