This is just my personal opinion, but i should to say my few cents about it:
Looks like you guys don't even understand HOW IS BIG AMOUNT OF WORK need to do
You do not even answer to yourself -> for what do you need to do it? Because some knows better C++?
You do not even answer to yourself -> HOW WILL YOU DO IT? Or you will keep c based functions in C++?
Do you even understand, that you CAN'T change C to C++ easy as 1-2-3, and C++ project it's TOTALLY ANOTHER EMULATOR
First few years (2-3) you will just try to convert C functions with C logic to another language.
Then next few years you will understand that you have builded C code on C++ what you have before
I really want to say a lot of words, but the main question? For what? Why not Rust? Why not GO? Why not python? What do you want to get in result? More bugs, more work, bigger time window between latest kRO episode & current rA? Or do you want just death of rAthena? What C can't do right now for you in code? Maybe it's time to better optimize C code and current functions and split millionlinesfunctions to small compact 60-70 lines function with deep & good parameters checks? Maybe it's better start to write C unit tests? I really trying understand your logic in your wishes, but i can't. Because C is hard, C in few things more limited then any other languages, but with C++ you will have million of problems with memory usage, etc things... Anyway, i respect your opinion about switching to another platform, it's ok for me, and i can't say you stop not doing it, but please think about it very well first, because looks like you guys don't even know what you are building, and i hope you will not waste a lot of your potential, time, and energy to trash.