If I may suggest something, because this parameter has been discussed for many, many years.
In an ideal world, the algorithm calculates the remaining time based on the altitude profile and the user's average speed on a given slope from previous activities. This used to be almost impossible to code, these days with AI it would probably be easier, but it still sounds super complicated.
So Suunto went the easiest route and calculated "ETA" by simply dividing the remaining distance by the average speed from the last kilometer. Of course, this is a huge simplification, because the speed on the approach differs significantly from walking on the flat or descending, and it resulted in the situation where at the end of the approach to a steep peak it would report 5 hours to go, and a moment later on the descent it would suddenly turn out to be 2 hours.
It was possible to use this if you knew the counting system and took it into account, but I was never a big fan of this information, it always told me more about how many kilometers were left to go.
However, it always seemed to me that the solution was relatively simple and at the same time satisfactorily accurate. As you can see in the screenshot above, the Suunto route planner predicts that at a speed of 3km/h the entire route will take me 6h19min. However, the value of 3km/h is default and can be edited, I have never done it, because the only place it is visible is in this planner, it does not affect the values on the watch later. But... if the user were allowed to determine their expected average speed on the approach, on the flat and on the descent, and then these values were applied to the altitude profile, it seems to me that it would be accurate and valuable. Then, as the route progresses, the watch would calculate how much ascent and how much descent if left and use the set speed values to calculate the remaining time.
I don't know anything about coding, so I don't know if it's easy to implement or not
PS - either way, the greatest value for me is the distance to the set POIs because I know how long a steep ascent will take me if I have 2km of it left, or how long I will descend if I have 5km left.