Let’s say that we believe in the literal meaning of Midrashim. Let’s also say that we aren’t learning like the Rambam (Hil. Melachim 12:1) that, for the most part, the Messianic future will be the same as this world.
Given these assumptions, we can follow the various sources about cool things happening in the future literally.
One such source is Avodah Zarah 5a:
וא"ר יוסי אין בן דוד בא עד שיכלו נשמות שבגוף שנאמר (ישעיהו נז, טז) [כי לא לעולם אריב ולא לנצח אקצוף] כי רוח מלפני יעטוף ונשמות אני עשיתי
And R’ Yose said: The son of David will not come until all Neshamos are completed in the flesh, as it says (Yeshaya 57:16), “For not forever will I fight, nor until eternity will I be angry, for the spirit before Me will delay, and the souls I have made.” (Translation follows Rashi here and Yefeh Anaf to Koheles Rabbah 1:13.)
So all souls are created. Great. Now what? The good and cleansed come back to life, the bad gets “judged” by the sun (Koheles Rabbah 1:11). What about future generations? There can’t be any more generations, as they have already all been born. But the Torah also commands us to procreate (Bereishis 1:28), and the Torah is eternal, never to become nullified. So what will be with the mitzvah of priah u’reviah, if bearing children is impossible?
(Granted, people in this world are also exempt because they’re unable to have children. My question is if in the future that will be the case, worldwide.)