Kdiff3 / gvim and other popular merge tools have 4th pane when doing 3 way merge (in git).
Could you please add 4th pane please? (The 4th pane in the bottom)
I'm honestly having trouble with that screenshot, but I *think* that the bottom pane is the merged output? in which case I think what you're asking for is instead to add the middle pane (i.e., the common ancestor).
That seems like a big change to our merge model, which is to present the two sides and the merged output as the central pane.
Have you tried starting a conflict resolution from Meld itself (i.e., running `meld .` in the repository where you have a conflict and opening the conflicting files)? That gives you an IMO better view where the middle pane shows the pre-merged code, but substitutes the common ancestor for actually conflicting chunks. I realise that this isn't what you're asking for, but it *might* be good enough.
cheers,
Kai