While I routinely exceed EPA rated range on most driving, save for high speeds on road trips, the problem with the rated range number is that many people have a tendency to assume that it is how far the car can go, but that's only true if driving at EPA efficiency. Rather,
rated range is a measure of battery capacity or SOC [State Of Charge], that is, it is a
fuel gauge. That's why it is best to just switch to displaying %SOC and skip rated range, unless trying to measure current battery capacity, a way to track battery degradation (my car battery is down 20%, based on rated range at 100%, over 127,000 miles since new).
Your suggestion to have the car "estimate range" would be difficult to implement
usefully, unless a navigation route is set, at which point nav
already does that very well by giving the real-time estimated battery percentage at destination, a hugely useful number for road trip legs.
"Estimate range" based on current or recent usage numbers isn't useful because it won't help with changes in terrain or changes in speed. A number based on traveling at the same speed on a road at the same slope is scarcely useful and would be even more misleading than rated range as a fuel gauge if you changed speed or the road's pitch changed. Nissan tried to do this with the original LEAF and it became known as the "guess-o-meter" and had mostly entertainment value.
Consider, for example, this plot of energy consumption for the last thirty miles of driving:
^ The estimated range of 219 miles is based on a usage of 211 Wh/mile, versus the 300 Wh/mile EPA standard for my car (a 2014 Model S-60). Is that a useful number to know? The only way I can get 219 more miles out of that SOC is if I continued to go mostly downhill for that distance, which is impossible where I live (and anywhere else in the USA, so far as I am aware). Is that estimate of range, based on the last thirty miles of usage, a useful number to know? I don't think so.
Regardless, if you really want your car to estimate range based on recent usage, all you have to do is turn on the energy consumption screen and set it to your preference of 5, 15 or 30 miles. Have fun with it!