Possibility to see where in the training was each (Power/Heart) zone
Whoop does this with heart rate zones, it shows how long you staid in each zone, and once you click on the zone, it shows on the graph the moments on the training where that zone was being worked. This is good to understand if the actual training achieved the zones required. This can be done based on Power Zones and Heart Rate zones.
Catherine Daly commented
I think this would be a great addition - it would be very useful to see what side of the zone you are on, for example are you on the lower end of zone 2 or just peaking in to zone 3. Even having the option to change the HR graph on the existing graph so you can see the colour change per zone