Andy C: 

To some extent it would also be fairly simple to convert/upgrade the existing housing stock, 

Actually not, it turns out, for general reasons. Keeping even existing installations in developed countries up to date is a major issue. I have a set of slides from the German electricians' professional association ZVEI on this, from 2012.

As a rule of thumb, housing electrical systems in Germany are supposed to last 30-35 years. As of 2012, 70% of building electrical installations are older. 

A Master's thesis by a student of mine looked inter alia at this question for his small town of residence. Only a quarter had modernised their installations in the last twenty years, and only a half in the last forty years.  In France, the situation seems to be even more concerning. 

It does concern the electricians' association (which in Germany is different from the electrical engineer's professional association VDE) that there is heavily increased use of electrical appliances over the last forty years, a situation which most existing installations were not designed to accommodate. A third of all building fires have electrical-system origin (figures from 2010), and building fires cause ~600 deaths (and - the pyramid again - 6,000 bad injuries and 60,000 light injuries) per year. So we are (were, in 2010) looking at 200 deaths per year because of electrical fires. This is an order of magnitude greater than deaths by electrocution (and quite a few of those are people clambering around on wagons in rail sidings who get too close to the overhead lines). 

This is likely going to get more problematic. PV+battery systems are attractive. PV cells have some flammable parts which can ignite when insulation is degraded and spot temperatures occur which can be achieved in installations in some warmer climes (I understand this has happened more than once). You really don't want a fire in the PV cells on your roof. Not only that, but what happens to the Powerwall in your basement when your house is hit by lightning? And what happens to your basement in consequence? I am not sure that we have got to grips safety-wise with all this yet.

Andy C: 

To some extent it would also be fairly simple to convert/upgrade the existing housing stock, 

Actually not, it turns out, for general reasons. Keeping even existing installations in developed countries up to date is a major issue. I have a set of slides from the German electricians' professional association ZVEI on this, from 2012.

As a rule of thumb, housing electrical systems in Germany are supposed to last 30-35 years. As of 2012, 70% of building electrical installations are older. 

A Master's thesis by a student of mine looked inter alia at this question for his small town of residence. Only a quarter had modernised their installations in the last twenty years, and only a half in the last forty years.  In France, the situation seems to be even more concerning. 

It does concern the electricians' association (which in Germany is different from the electrical engineer's professional association VDE) that there is heavily increased use of electrical appliances over the last forty years, a situation which most existing installations were not designed to accommodate. A third of all building fires have electrical-system origin (figures from 2010), and building fires cause ~600 deaths (and - the pyramid again - 6,000 bad injuries and 60,000 light injuries) per year. So we are (were, in 2010) looking at 200 deaths per year because of electrical fires. This is an order of magnitude greater than deaths by electrocution (and quite a few of those are people clambering around on wagons in rail sidings who get too close to the overhead lines). 

This is likely going to get more problematic. PV+battery systems are attractive. PV cells have some flammable parts which can ignite when insulation is degraded and spot temperatures occur which can be achieved in installations in some warmer climes (I understand this has happened more than once). You really don't want a fire in the PV cells on your roof. Not only that, but what happens to the Powerwall in your basement when your house is hit by lightning? And what happens to your basement in consequence? I am not sure that we have got to grips safety-wise with all this yet.