Definitely, it's the end of an era (or getting towards it). Those three are all-time greats, and it was bizarre to have them all playing at the same time. We've been waiting for years for the next big player to step up, but understandably no-one has been able to match these three so far. But at least it will be interesting having diferent winners all the time, with no-one really dominant.
Maybe when they really go out and say that they are retiring, we could see players becoming the next big 3. But Djokovic is still active, and Nadal trying as well and maybe we can still see Federer next year too.
Perhaps after they 'officially' call it quits, Medvedev, Rublev and Tsitsipas can comfortably claim the next big 3. They just need to step up and starts to win Grand Slams.