Fed winning another major at 38 would put more butts and more media coverage than CYGS.
It would not really generate more coverage than his 2018 AO, when he was already 36... there won't be much difference for the general audience.
The greatest story that could be had with late-career Fed was his 2017 comeback at AO, and his overall season (with WC following as a confirmation). He hadn't won a slam since ages, he was coming back from injury, considered "old" at 35... many thought he'd never win a slam again. Yet, he proved otherwise, defeating his nemesis Nadal after an epic 5-setter.
You can't beat that. And you won't.
In terms of storytelling, a 2019 Fed win (more likely to happen at WC) would feel déjà vu.
There's only one case where a Fed win would make big headlines: at RG after beating Nadal. I'd highly doubt it would happen...
Nole slam did not get any coverage/hype it deserved. A CYGS will get better coverage but there would be stories of how Fedal are old, no new challengers , etc., all watering down the achievement.
The 2016 NCYGS got eclipsed, in terms of storytelling, because it was Nole's own CGS as well. And, whilst hugely rare in the men's game, NCYGS isn't uncommon in the WTA...
A 2019 situation would be different, it's the 50th anniversary of Laver's CYGS. And nothing would "pollute" the storytelling this time. I'm even pretty sure that media will recall past CYGS, as well as past failed attempts (remember R. Vinci...).
I have no doubt that Fed winning another major will get more viewership and coverage.
If it really were the case, I'd say something would be hugely wrong in the kingdom of tennis.
A CYGS should be a much bigger event than yet another slam from someone who already has 20 and won his last one a year ago...