Novak Djokovic's PTPA is not looking to replace the ATP but would consider it if suitable offers for something like that arrived.
The PTPA was formed by Djokovic and his good friend Pospisil as they felt the ATP was not doing a well enough job of representing all the players. While receiving largely negative reactions, the organization received some support from fans and even some seasoned professionals like Isner, Schwartzman, and Opelka among others.
In a recent interview, Ahmad Nassar, the executive chairman of the PTPA shut down talks about replacing the ATP but would not rule it out completely:
"I think the sport overall of Tennis has some decisions to make. I think we’re very fortunate to have the example of golf right now to say, ‘well, is that what we want for our sport?"
He continued:
"When the PTPA was created a few years ago, there was a presumption that ‘oh, this is a rival tour; this is the only logical conclusion: that the PTPA is a rival tour’. A big part of what I’ve been trying to do over the last few months is to dispel that notion and say, ‘that’s by far not the only logical conclusion. I’m not sure it would ever make sense for a players association to operate its own tour?"
But then he added this:
"Would we partner with other people, would we negotiate with others? Absolutely. That is our job. We’ll negotiate with anybody who wants to employ tennis players, we’ll negotiate with anybody who wants to do things on their behalf, whether they’re sponsors, licensees, events, or any other types of opportunities for the players. Because that’s why we exist and that’s why the players created the organisation."