Construction costs are currently skyrocketing

You forget that the current gas condensing boilers will probably not last another 30 years. These are not old oil heating systems that always work, but are already packed with electronics. If it really happens in 2024 that no fossil fuels are allowed to be installed in single-family houses, many many people will have to give up their houses, for which they have saved and paid for decades. Then probably also for poor prices due to the oversupply, so that the classic retirement provision home breaks down for an entire generation. Subsidies for the corresponding renovations are basically rubbish anyway, as they are already priced in by the companies. The shortage of skilled workers leads to further increases in renovation costs. 15k for an air-water heat pump is completely exaggerated. There are already top devices on the market for under 5k. The markups of the companies are cheeky and will remain so. I only hope that the coalition government finds a socially acceptable solution. Otherwise, I fear the worst in the next federal election.

I hope it doesn't lead to many elderly people having to leave their homes because they cannot afford the switch to a heat pump system. Presumably, there will be exceptions in these cases.

I'm not quite that pessimistic. There is currently also the existing protection for oil heating systems. They can be over 30 years old but only need to be replaced when the house changes owner. The critical point is when the heating system breaks down and must be replaced unexpectedly. However, politics could certainly help with appropriate KfW loans. A low interest rate and a certain generosity in granting loans, especially regarding pensions, could certainly help many people. The question is whether such considerations play a role and how far politics should be conducted with the people instead of with ideology. I do consider Habeck a realistic person, but politics is more than just one minister.

Then there should actually be hope that the prices for oil heating systems will drop significantly in the near future ….

In a building with a heating demand over 100kwh/m2 (older, no underfloor heating) that will not work. or you can just put 5*2kw DIY store fan heaters for 29.99 each in the building and heat with electricity

That is complete nonsense. The heating demand of a building is independent of the type of heating, and of course a heat pump can also provide that much heat for an old building. And it has nothing to do with fan heaters, because the principle of the heat pump is used. The efficiency is about a factor of 4 higher than that of a fan heater.

Then there should actually be hope that the prices for oil heating systems will drop significantly in the near future ….

The problem will more likely be finding someone to install the heating system... Some will surely panic now.

If you are even allowed to install the oil heating system anymore.