I didn't see anything in there about penalties for carriers not enforcing this. Also willing to bet they beg for extensions claiming they're not ready - or too costly to implement.
All the major carriers are implementing a STIR/SHAKEN strategy that should be in effect by next year. But it is complicated to do and there may still be problems when they do - as others have explained here it's not as simple as it first appears.
I don't have any sympathy for the operators in this. They've profited from this for long enough and ignored the problem. There's a lot of pressure on them to solve it and the impression I have is that there's no appetite for "the dog ate my homework" excuses from regulators so let's see.