The fact that we've had complaints from players and DMs of the 5 (or 15) minute workday in AD&D, 2E, 3E *and* while playing 4E pretty much tells us there is NOTHING that can be done. You know why? Because every DM is different, every DM designs his combats and adventures different, and every reason why "going nova" occurs to a particular game is completely different. It's NOT POSSIBLE to fix the issue, because there is no ONE ISSUE to fix.
All we need to see to prove this point is the incessant arguments here on ENWorld about things like how punishing the PCs for resting is lauded by half the players as a good way to condition them not to try and rest often and in any location... while the other half gets mad that they feel as though they are playing a "metagame" by artificially throwing extra combats out there, not because the story asks for it but purely as a punishment. And this is two opposite sides on just a single idea to solve the problem. Every other idea possibly offered up has the same amount of proponents and opponents. WOTC CAN'T WIN.
Even if WotC was to design and offer up in the DMG three different game mechanics in an effort to combat the "5 minute workday", we'd still get hundreds of players complaining that they didn't solve the issue. Even if they offered up FIVE different modules to try and rectify it, that still wouldn't be enough. Many players would still find ways to go nova within the confines of whatever style of game the DM was playing, and the DMs would have to figure out ways to deal with it.
The ONLY thing that can be done is to admit that there is no way to solve this issue, because like I said, there is NO ONE ISSUE. The "5 Minute Workday" is not an issue. It is a symptom of DMing Style, which is truly the issue. And you can't "solve" DMing Style-- because no DM cops to the idea that how they DM might really be the issue for why things they don't like keep happening.