Let's think this through.
Broadcasts airing on free-to-air television are currently not under OFLC. An R-rating would be silly, and would make it harder for parents to tell which shows are full of, say, chainsaw massacres and which shows have somebody having a smoke. But it wouldn't be crazy bad. I generally ignore ratings, whether OFLC or from the broadcasters, and go with IMDB's parent's guide if I'm in doubt anyway, and expect others do too.
That changes when we think about how TV is shifting. OFLC claims jurisdiction over streamed broadcasts and DVDs. And when OFLC issues a restricted rating, you can be subject to large fines or jailtime if you provide access to an R-rated programme to someone under the legal rating age. Showing an R-13 film to someone who is 12 carries a maximum penalty of 3 months in jail or a fine of up to $10,000.
So if the proposal extends to streaming and DVDs, Spiderman cartoons from the 70s would be R-rated because of J. Jonah Jamieson's cigars. If it went to film from just TV shows, so would the old version of Pinnochio that has him turning green from a cigar.
Sure, prosecution might be unlikely, and judges might be reasonable. But NZ's censorship regime is nonsense; R-ratings for 70s Spiderman would put that nonsense on stilts.