"The problem is that you can't change the nozzles at every place at the same time."

This was exactly the problem we had the last time.  People aren't allowed to modify or work on gas appliances.  It has to be done by an approved technician.

In the 60's there were far fewer users of gas appliances than there are now.  The changeover would be immense.

What would drive the decision would be the selling price of the gas.  If it is high enough then it will be economical to build FT plants.  If not then conversion might be cheaper.  Remember what we're effectively doing here is comparing capital costs (for FT or conversion) with ongoing inefficiency costs.  History has shown that lower capital costs will win if we can accept the higher running costs.  Especially if these can easily be passed on to the final consumer.

There is also another issue with Town Gas.  It is very poisonous.  The CO content can easily asphyxiate someone if there is a gas leak.  Indeed before Natural Gas ovens a common method of suicide was to stick your head in a gas oven and turn on the gas.

With Natural Gas all you get is a splitting headache and you'll maybe pass out, but you won't usually die.

Because of this I think there would be a central government & consumer preference for "safer" natural gas.

That said, I think there is definite scalability issue with this route.

"I would also expect to see the complete decline of Natural Gas electricity generation.  Plus many households may transition onto storage type heating using surplus Nuclear electricity generated during the night"

"This is a very important observation, though I don't know any system that allows you to do that."

In the UK there are many common storage heating systems used in houses and flats.  Indeed my house used to have a storage type heating system until I ripped it out and threw it in the local dump.
They operate on the priniple of heating up large heavy ceramic bricks and then allowing them to release their heat when electricity is expensive.  Unfortunatly they are difficult to control and are ugly to look at.
Mine met their demise due to their age and cosmetics.

I now run direct heat electrical resistance heating.  I try not to run it at peak periods.

Andy

Storage heating systems are very popular in Bulgaria. I don't find them ugly, and besides they allow some small joys like sitting on them to quickly warm up after entering from the outside.

What makes them popular of course is the price differential which is about three times higher rate for day vs night electricity usage. And then the underlying reason is that most of the generation comes baseload nuclear and coal. No natural gas in Bulgaria. Hydro is used for balancing, but the need for demand side management to smooth the peaks is also obvious.