Final Fantasy VII: Remake got a pretty major expansion called Intermission, which added both the fan favorite Yuffi as well as her story. But even if this turned out to be a popular solution (although helped by the fact that it was included with the Intergrade version), it does not seem like we should expect something like this from the upcoming Final Fantasy VII: Rebirth.
The director of the game, Tetsuya Nomura, recently talked to Vandal and revealed that Square Enix "are not planning any DLC for this installment". Considering how long time we had to wait for Final Fantasy VII: Remake (announced 2015 and released 2020) and now Final Fantasy VII: Rebirth, it makes sense that the team would focus on getting everything done instead.
And since Rebirth is said to offer over 100 hours of gameplay, we doubt there will be any shortage of things to do regardless if DLC is added or not. It will be released exclusively for PlayStation 5 on February 29.