If you're being called from a local number, then this should mean (and outside of USA actually means) that there's somebody who's subject to local law and fully responsible for ensuring that the spam laws are met. If you're a telecoms operator sending in calls to the nework, then you ensure that the fines get paid - the spammers are, naturally, liable, but if you enable access to scammers in an unreachable jurisdiction or insolvent shell companies, well, it's coming out of your pocket and it's your problem on how to recover these losses. In USA, however, telecoms who specialize in providing such access to phone spammers have a legal and profitable business model. This needs to change.
CID spoofing is when you tell the network to display a different caller ID value than the actual originator. This never had any sort of authentication in the US (until the announcement in the OP)
Most of the spam calls in the US aren't CID spoofed, but some egregious scams are. This is usually used for things like scammers displaying "SOCIAL SECURITY" on the caller ID.
The US just generally doesn't make carriers liable for the crimes of their users. We don't need to change that, and I don't think it's a good idea either because of the unintended affects that could have on accessibility. We just need to require controls that authenticate proper use of the network. The announcement in the OP is one step towards doing that.
But preventing CID spoofing alone is not going to stop spam calls from local numbers, because VoIP.
Back in the early 2000's I remember doing the same thing you're describing: startling spammers by telling them that I was on the list. But today, the people calling don't care because they aren't inside of the US.