I don’t think my large number idea is feasible. XMB has reached the maximum memory supported on Connect IQ for most Edge devices. Something would have to be removed to add any new feature.
As long as you are hitting the target watt range indicated for work and rest intervals, the buckets should fill in near equal proportion.
That assumes you decide to perform the interval portion of your ride after a warm-up, but you could do them at any time during the ride.
For endurance rides the goal is to stay within 75-100% of your LTP to raise Zone % (percentage of time in that zone) and for the bar above Zone to show mostly blue. Below and above that “zone” will show as black on the bar.