Please do literally nothing to the case, just release it as is
As I understand the intention behind the C4 was to accommodate the most powerful components. And since the GPUs are getting bigger, it is natural to increase the case size to accommodate the new top end GPUs. This is my opinion, but not everybody will agree of course.
This is a tricky call, both these points of view have merit, and I can see that @dondan is in a potentially difficult position again.
The C4 has been evolving for the last 5 years and is nearly ready to go.
The pressure to develop it yet again is a bit like holding out for the next generation of CPU or GPU, there's always going to be a new one soonish.
In either situation you have to draw a line in the sand and commit to buying something.
Personally, I am not worried about the latest/greatest kit as I don't want to spend out large amounts for disproportionately small gains.
I am mostly buying used kit these days, and am happy with 2nd tier performance and be left with money available to put into other interests.
I am not convinced that sub 20L, let alone sum 15L cases can and should be expected to be able to cope with the most powerful and hottest running components, with ITX rigs, something has to give.
There is always a compromise with conflicting requirements of small size / power / quiet running
I personally think the RTX 4xxx huge power requirements are madness, especially with energy supply problems that are with us. If anything, I want something more efficient and lower powered, not a kW guzzling setup that is overpowered.