If you look at what is happening as the infinite future of the brand, then you've got to set yourself up for future flexibility. In the long run, the segment of brand's historical portfolio will become only a small portion of the site. The 2009-2014 will become a small subset of information and a niche group of users. As will the 2015-whatever the next refresh is. The pie gets bigger, the slices get smaller.
From what I've seen in other places, forum & sub-forum are the way to go. you become Genesis Owners in the sense of the brand, and not the model(s). Genesis forum becomes the generic "off the top" primary heading then >G60, 70,80, 90, and 2009-2015.5 (or whatever year it lands in) Hyundai Genesis as sub-forums to that forum. If they do major stratifying within the models (like BMW's 3 series in both Sedan and Coupe), you can then sub-sub-category within the parent model.
For comparison sake, maybe compare something like Yotatech to 4RunnerForum. They've endured and kept up with several refreshes, new models, re-labeled products (lexus SUVs), and still manage to present the forums in a useable way.
Another place to look for structure ideas would be motorcycle communities. You wanna see a new models/refreshs/old models/name changes nightmare? There's probably more than a few sites who have built a structure that keeps all relevant info organized... or at least, findable?