Up to now I have been requesting the addons/themes list in a profile be restored. However, ‘More by this Developer’ would be a big improvement on that, so your suggestion gets my vote.
I suspect it may actually be easier for Portland Labs to implement as ‘More by this Developer’ would be contained within the marketplace sub-site (and one of the reasons given for loss of the addons/themes profile list was the difficulty of making queries across sub-sites ).