The problem is that it is a very useful feature for mixing.
This indicator gives you a clear indication of the delta level compared to the previous automation pass, so that it is very easy to punch out without creating level jumps and without even using the cross-over mode.
Sure you can do the same thing watching at the curve real time update, or you can rise the return time but i find that it's really easier and more precise to watch for the delta indicator. Because it's two colors, you always know if you are too low or too high. Not as easy watching at the curve.
When mixing it's important to concentrate about what you ear, the less distraction with complex curves and computer things, the best you can mix. That's why for example using a mouse is not the best thing for mixing you can loose too much concentration in watching the screen and manipulate precisely the mouse to turn buttons or to do precise tasks.
I don't think that the feature has been silently removed, if it were the case it would have been announced in the changelog and the manual would have been updated. I think that it is a forgetting perhaps after some automation code updates.
It seems to me important that a software giving sample accurate automation can give a good level of user visual aid to have some benefits from this accuracy.
Some users are focusing on technical things, like the multiple discussions we can see talking about the usefulness of 32, 48 or 64 bits mixing engines. The most important is not here as soon as you have a descent audio quality and all DAW have that today. The differences are in the user GUI and control interfaces. This missing delta indicator is a regression for me.
Same remark for the interface inconsistencies between the mixer and the channel strip. Why the mixer is using a newer design a la Ardour, when the channel strip is still using rotary buttons ? This for sure is confusing users.
All those small but important things are suggesting that version 6 has been developed in a hurry to fit the Nuage control surface as soon as possible.