Exterior wall for KFW 40 (+) with or without ETICS?

Our ancestors probably thought the same thing 50 years ago. Energy cost nothing.
Who knows what will happen in the next 50 years.

That's definitely a difference. Zero is a hard limit for heat loss in a building. In practice, heat will always be lost because you have to exchange the air from time to time and people have to go through the front door. Even if you improve the 90% heat recovery ventilation again and halve the loss, there will still be some loss left. A house with <=25 kWh/sqm will still be fine in 50 years. Technically, much more is already possible today, it's just neither financially nor environmentally sensible. And the topic of saving CO2 through more efficient heating will soon lose political relevance. Simply because in 20 or 30 years the electricity will no longer come from coal power plants.

Real energy will no longer interest anyone; it will be very cheap to acquire, and houses already need very little energy. It will be more about peace and saving costs. We will see completely new construction methods that have almost nothing in common with today's houses.

Exactly, since the Plus Energy Amendment of 2035, electricity has been mandatorily generated by private households. Vacuum insulation is mandatory from 2040. Those who have a negative energy balance in their household will be heavily taxed. The KfW provides 1 Bitcoin as funding for the energy-efficient renovation of these old buildings.

Well, honestly, this timeframe is not foreseeable. Everything is speculation. However, I consider it wise to learn from the past. What will actually happen, we do not know.

Learning from the past is never wrong. But you also have to be careful to draw the right conclusions and consider certain limits. The topic of insulation is almost fully exhausted with KfW40 and completely with Passive House standard. Other topics will come up; a photovoltaic obligation already exists in many new development areas, and it has also been frequently considered loudly for existing building renovations. Here in BW, this is already half in place: anyone who replaces the old heating system must contribute renewable energy in some form (solar thermal or photovoltaic) or insulate significantly more. This will certainly become mandatory in the coming years.

Heating with fossil fuels will also be pushed out of the market in the coming decades. The CO2 tax is only just beginning, and CO2 targets will only be achieved if prices are significantly raised. This will certainly take longer than the photovoltaic obligation, as many large apartment buildings can only be economically heated with oil/gas for the foreseeable future. However, the trend is clear, and once the CO2 tax instrument is established, it will be much easier to adjust prices.

Exactly, they will manage it, that building a house is becoming unaffordable for average earners. These salon environmentalists and red wine sippers.

After the passive house, nothing will come quickly. Any more and the waste heat from people will become a problem. I think in the future there will be technology such as better heat recovery with 99%, windows that let solar gain in during winter and less in summer without shading. Methods that keep houses cooler in summer without air conditioning, warm in winter, heat pumps with an annual performance factor in the double digits. Walls of the passive house will become thinner.