Regarding the change, I'll post my comment here.
Cool! Looking forward to it.
I typically don't use Review tab's Show Line, but prefer to go to the Analysis Tab, one move prior. This shows Show Line's line if in the top 5 and other relevant lines. This is more informative as I toggle between Review and Analysis and get a better overall appreciation of the positions.
An Example:
After d5 Review' tab's Show Line:
Prior to d5 Analysis tab's presentation:
I get a lot more out of seeing/reviewing Analysis's 5 lines, than seeing the result of the line I took.
In addition to the Review's Show Line display offering a Show Alternate Moves could be really useful.
Show Alternate Moves to d5:
I tried to comment on https://www.chess.com/forum/view/changes-to-show-line-in-game-review
and got a 500?? sever error.