“It’s also not really a limitation in many cases: how often do you actually need to take the address of something?”
In C++ a const T& parameter forces a value into memory so it has an address, even when it would fit in a register. Carbon lets the compiler pass small values directly and makes you ask explicitly for an address. That is a real performance win hiding in the boring part of the spec. It also shows how much speed C++ leaves on the table for compatibility.