There is a famous Ran on this gemara who proves that it is assur for one to reveal a family that has a mamzer in the family. In the future, even when it will be possible to identify the p'sul, the family and even the individuals will remain mutar. The Ran does suggest that tzenuim who know about a p'sul in the family should let their friends in on the secret privately because the family doesn't qualify as a mishpacha miyucheses, but they should not tell others. At first the Ran questions whether the heter of being metaher families with pesulim mixed in applies now or only l'asid l'avo, in the end the Ran concludes:
וכיון שאין אליהו עתיד לגלותן, אף היודעים בהם עכשיו אין מגלין אותם שאין בין העוה"ז לימות המשיח לענין זה כלום
Meaning, that nothing can change between now and then, therefore if they are mutar then they are mutar now.
R' Moshe (Even HaEzer 4:9:3-4) offers 2 possibilities in understanding the Ran. Why is the issur of marrying a mamzer different than other issurim in the Torah? Just as one is obligated to prevent their friend from violating another issur in the Torah, they should be obligated to prevent their friend from marrying a mamzer, and not cover up the p'sul!
A. The issur of marrying mamzeirim and other p'sulei yichus is dependent on the knowledge. Although by most issurim we consider the lack of knowledge to merely be an o'nes, but not an actual exemption. In this context, we truly follow "what you don't know won't hurt you". The issur is only realized through ye'diya, and without it there is no issur. Based on this, one should technically not reveal even a private individual who they know to be a mamzer and is not mixed up into a larger family. However, Chazal were concerned that it will cause a takala in that even people who know will marry them, so they require one to tell about an individual who is a mamzer, but not to tell if the mamzer is mixed in with kasherim.
B. It is not the knowledge that is matir, rather it is the ta'aroves that is matir. If one can identify an individual who is a mamzer, they are obligated to identify him, but when that individual is mixed in a family, the ta'aroves of the kesheirim with the pesulim will be matir the entire family. Once the ta'aroves occurs, and is not able to be identified following rules of Rov and Chazaka, he is permitted even if he can be identified by Eliyahu through Nevuah. Therefore, if witnesses know about an individual who is a mamzer, they are obligated to reveal, but if they know about a family who has a mamzer mixed in, their revelation won't have any affect since the mamzer remains mixed in with kasherim and can't be identified.