The first expected accessory if the MacBook features OLED Touch Bar
MacBook with OLED Touch Bar is in rumor, and MacOS Sierra API Differences has also hinted the same. If this happens, the top Keys line with functions button, volume button, power key etc. may be removed. Many users may want to get the physical keys back, so the first expected accessory for such model would be the missing keys that OLED Touch Bar will replace.
Based on this rumor and expectation, Martin Hajek has made a concept design how such accessory may look like if it really happens in Future. Here are the images;