I mean OGS has that part too for the actual chat, just not the review text box.
There is also a play button (or press ‘space’ I think) which you could press at the start of a branch/variation and it will play out the main line from there 
(you can change how fast the stones get placed in settings)
One could give the stone a similar blue rim/box shadow on the board either if one wants to build the association between “this move in the tree has a comment” and “this stone one the board has a comment”.
Of course that won’t tell you when there’s a branch. Maybe some comments will only be in the middle or end of branch variations.
Maybe something like the exclamation or some kind of branch symbol (like the GitHub fork one) could indicate branches
These kinds of guys
