That's a very bold assumption... These are mutants we are talking about for all you know there are mutant men that can give birth, or tans men or non Binary mutants and such. It's also more of a oh so having more mutant babies is like very encouraged but not a by force thing.
From what we've seen in the text, 'Make More Mutants' seems to almost entirely been in the hands of the Five, who have made *many* more mutants during the age of Krakoa than the ladies have produced with their uteruses.
But Apocalypse has them all beat. He 'made' millions of new mutants by inviting the Arakki to Earth. The Five are going to have to resurrect all of Genosha to catch up to that feat.
Meanwhile, Lucinda Guthrie just waves it off. "Make More Mutants? Already did my part. I'm just gonna sit this one out."
*Supposedly* Hope and Wanda used the Phoenix Force to undo at least some of the effects of the Decimation, back in the day. Maybe Jeb was one of them, since it sure didn't seem to affect a ton of other named mutants who mysteriously remained Decimated?
And yeah, it would be neat to see Jeb's unclear power get explored (some sort of blue cold energy plasma that looked like lightning or fire, but didn't burn the kid he used it on, so it could have been cool energy plasma, or illusion, or who knows!). And also to see Elizabeth get her 'Amazon' size-changing powers, first hinted at in Age of Apocalypse.
And hey, maybe Cissie, Joelle and Louis can get mutations, and that mysterious nameless tenth girl can get an actual name!