We face this same problem for some of our projectes (not all of them). For this cases we’re not using Craft, but the Brand.ai plugin for Sketch, which allows you to create versioned releases of your artboards and assets.
Anyway, our longest projects finish about 6 or 7 design cycles and design releases. I can’t figure if even Brand.ai would fit a lifetime continuous-release design project (though it seems so).
The only ‘problem’ with Brand.ai is that you can only create a single library with the free plan, and the ability to create multiple libraries comes with one of the most expensive ones (about $100/mo.).
If you give it a try, please let us know how did it work for you! :)