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Could these be the beginning of a new "Famous Americans" series?
I doubt it, as the commemorative format is not typical. Usually, a "Famous Americans" series would be a regular issue format; not a commemorative.
Interestingly, I looked up the biographies of the four Scientists depicted and while they have no doubt made important and significant contributions to their field, the names are rather obscure to most Americans not familiar with the sciences; two were born outside the US but later became citizens; and all but Asa Gray were awarded Nobel Prizes.
As I said in my initial post, the printing of 30 million stamps is less than 1/3rd the printing of other "Forever" stamps and that, too, would be indication that they are not intended to be an on-going series of stamps.