This could be implemented by:
- importing the remote revision and displaying it as a ve.dm.VisualDiff;
- then, if the user chooses to proceed, converting the remote revision into a single ve.dm.Change that applies to the common base document (=the document at the start of the edit session);
- then rebasing that change against the current document's completeHistory (=the transactions that correspond to the changes during the edit session), before applying it;
- then applying the rebased change.