Itll still be two sticks in the future. I just checked myself to confirm. Looking at even Z790 boards that take DDR4 the higher you go in capacity and slots used the slower the board supports. Its not a matter of DDR5 or not. Just dont run 4 DIMMS if you dont have to or if you prefer speed

Keep in mind this is the case for RAM in general. Even DDR4 and DDR3. As soon as you try to add more than 2 dimms you need to dial back the frequency or youll have stability issues. Its just common RAM knowledge