7-8 more for Djokovic, while definitely an optimistic scenario, is not that unrealistic, or have we not learned anything? He's 32, with no history of serious injuries (relatively speaking), no real signs of aging, and the best player in the world. So while I understand it's projecting 7-8 more slams can sound too rich (7-8 slams is like a hall of fame career on its own), I wouldn't rule it out, depending on how the rest of the year unfolds. I mean, he's a favorite to win the major taking place right now. I wouldn't bring up the next gen until I actually see that there is one worthy of being mentioned in this conversation. Only the big 3's age/injuries will stop them for the foreseeable future. Yes, "things can quickly change," except they haven't in 15 years. These 3 aren't any 3. They're literally the best three players in tennis history.
Athletes across every sport are performing at a high level at unprecedented "old" age and that's more or less a fact. So while years ago, predicting 7-8 more slams for a 32 year old would have been ludicrous, it's theoretically less so now. I say theoretically, because I'm not saying it's likely -- that's a LOT of slams -- but that he should be able to play at a high enough level to at least compete for them and be among the very clear favorites.