The way I see it is that VO2 max is only a proxy for potential cycling performance or any other aerobic sport. So if you are measuring cycling performance directly i.e. Watts/kg then a backward estimate of VO2 max is not really of much practical interest. My training App uses ride data to estimate W/kg over different time periods and tracks those automatically without any specific test protocols. It reports trends of my power and W/kg for endurance, threshold, max aerobic, anaerobic and sprint, which is far more relevant to cycling specific performance than VO2 max - either estimated or measured directly in a lab.