I think there are a couple of things to considerate here. First, DTM has always been about the german OEMs. Those brands won't support traditional motorsport with combustion engines much longer. These decisions are made by the boards and those are not interested in what the fans or drivers want. They will only pump money into electric series or series with hybird technology. And that isn't just true for german OEMs but motorsport in general, there is a reason why the WRC is going hybird, F1 already has it, WEC and IMSA are also going down that road.
So, if DTM shall continue with new cars, they have to be electric or at least use hybird tech. Funny thing is that DTM was going for hybrid engines as well in 2021 or 2022, but Audi decided the pull the plug anyways. Things are getting a bit complicated because hybrid technology is so damn expensive and electric cars are not that fast and not able to compete in endurance races. At the end of the day - just look at the WEC - all kinds of brands want to compete in big races like Le Mans, but they dont want to spend any money on it. And now there is COVID 19. Just great.
Is there a solution to all this? Maybe. The great thing about GT3 and GT4 cars is that the OEM dont have to spend any money on them. These are customer cars and its a fine business for the manufacturers. There are already talks about hybrid tech in GT3 cars or maybe all-electric GT cars. So if you start a new DTM with GT3 cars, you could switch to hybrid engines in a couple of years and full-electric engines a couple of years later. Costs would be dramatically cut compared to the Class 1.
Since ADAC GT Masters is a pro-am affair for private teams, the new GT3-DTM could focus on pro drivers and OEM-backed teams. Its not an ideal solution but it would secure the DTMs future. And then there is the DTM Trophy, featuring GT4 cars and non-pro / gentleman drivers. That is already the natural sub-class to a GT3 DTM class.