The royal WEEE ???
"Our models, our mental models, are wrong; we have been trading security for performance and complexity all along and didn’t know it," the researchers observe.
Oh really? Who's "we"?
Well there's a surprise. Not.
Memory access protection existed for a reason. Also, speculative execution mustn't change globally visible state before it is confirmed that the instruction will actually run to completion, otherwise Bad Things may result. Retaining the necessary attributes throughout the speculative execution process was probably a bit much for some chip architects and designers to cope with, especially if they wanted their chips to look good, fast, and cheap.