Is my thinking wrong, here? We need to figure out just which set of things to kick upstairs to the master template to be customized or tossed out as the site author sees fit.
context bar's a biggy. So are the headers that so many packages put out arbitrarily. I've done several sites where we've suppressed those by ripping code out of huge numbers of scripts where one could just leave them out of the master template if they're properties passed up the hierarchy.
Those are obvious (and have been discussed before, including very recently). What other page elements need to be kicked up to the master?
Remember that we're looking for a code freeze for 4.6 in a couple of weeks if possible. Most of our thinking needs to be for 4.7 (which will be blasting off for development right on the heels of 4.6).