It would appear that the first stage operational reusability is happening for multiple companies in the near future. The next step seems to be fairings and second stages coming back for more employment. It seems to me that there may be a possibility to use one to assist the other if there is enough payload margin. I am suggesting that the fairing be kept with the second stage all the way into LEO, or possibly even into GTO.
The payload fairings on most vehicles seem to be more expensive and robust that I had been aware of even a few weeks ago. I am going to suggest incorporating a heat shield into the fairing and using it to protect the second stage through reentry. It would appear that the mass of fairing and second stage would have a fluffy enough reentry profile that the heat shielding material would be a fairly minor mass hit compared to those on vehicles with higher density. The main mass hit would be that of carrying the fairing through the whole mission rather than the normal jettison at low enough dynamic pressure.
At payload separation, two arms on the second stage lift the one piece fairing off of the payload exposing it to space. That is cartoon 1 on the left with the arms in green. The arms flip the fairing around and pull it up over the engine and tanks as in cartoon 2. At reentry the stage is fully enclosed in the fairing with the engine mass forward in the pointy end as in cartoon 3. If it can be done this way, the second stage would see very little thermal stress during reentry and has the possibility of gas-n-go seriously enhanced.
Bonus points with the arms would be if they could be used for deploying solar panels and antennas for the spacecraft before deployment saving a bit of risk and complexity. More bonus points if the arms could also be used to deploy parachutes or other recovery gear at the lower altitudes.