That seems a rash claim. It has happened three times in my lifetime: are you expecting to die young? Do you claim some insight into what riders might, or won't, emerge in 30 or 40 years time?
You cant compare cycling from then its not the same at all and I dont expect cycling to become less competetive like those days. Usually thats not how evolution work at least, cycling is growing while were also in a golden era, more money, more desirable to become a cyclist, more talents etcetc.. But maybe a rash claim sure its a long time lets go with in a very long time then (but untill this year and Pogacar it was deemed impossible to just do the Giro/Tour double, true legends who have tried and failed just the Giro/Tour double in modern time say its impossible and up untill this year it was deemed almost impossible in what people call/categorize modern cycling)lets see.
Its certaintly been a while and cycling has changed since then and not for the easier(more specialized than ever. Imagine doing GT's vs specialist then going up vs a freak like Mvdp in the classics its a different sport almost), nevertheless its not something you expect to see very often. Should still make a Giro, Tour WC jersey to him for winning it all in same season, make one to Roche and Merckx too, the three musketeers.