​​​​​​Sure. But that's not a common interest. (I didn't say it wasn't ever useful.) It also wouldn't let you know how much more if there were inflection points.

You can also get that information from the relative elevation in the track file (if you are using one), which is how Garmin's "climbpro" works.

Accurate gain doesn't require accurate altitude. If the altitude is off by a constant amount over the course of a ride, the gain will still be the same.