Eventually chains and cogs need to disappear altogether. "Infinite speed" systems have been used for machinery since at least the 60's and probably earlier. It usually consist of a belt or chain riding between two cones. As the cones move apart or closer, the gear ratio changes giving you an infinite choice of settings between the minimum and max range. No more worries about how many teeth you step up from one gear to the next, so no unwelcome hits to your cadence output.

The technology is there but the price of materials strong enough to do the job and light enough for bicycles is probably lacking.