When multiple changes needed to be integrated between branches, there are advantages to merging each change individually rather than perform a 'bulk' integrate:
1) The target branch receives a more granular history
2) If there are conflicts they tend to be easier to resolve when only dealing with a single changelist at a time
3) If you link changelists to jobs, it's nice to track each fix individually as the fix is merged
4) Time-lapse view becomes much more useful in the target branch
This is actually the method recommended in the book "Practical Perforce" by Laura Wingerd:
"A very practical way to integrate changes between branches is incrementally - changelist by changelist, in order. This method preserves logical changes as they're propagated from branch to branch. In also keeps the problems of reconciling, resolving, and merging files to a minimum." - Chapter 4, pg 97.
Currently P4V can (optionally) perform the p4 integrate, p4 resolve and p4 submit (assuming no conflicts) automatically. However, this is a 'bulk' integration. If multiple changelists need to be merged, this process will integrate all files, across all the unmerged changelists into a single target branch submit.
I would be useful if P4V had the option to merge each changelist individually, halting and prompting the user to resolve only if conflicts are encountered.
Perhaps a good first target for this feature would be as a Streams only feature?
It would be nice for the this feature to automatically populate the merge changelists with the following format:
Merged @ from to :