For kernel dev it would be a disaster, there's too much implicit action, and abstractions that have unknown runtime cost. The classic answer is that everyone uses 10% of its features over C, but nobody can agree on which 10%.

As someone forced to get up to date with C++ recently, at this point it's a language in full identity crisis. It wants so badly to be Rust, but it's got decades of baggage it's dragging along.