This is something that's often suggested, but not practical, at least in a pistol of the same size.
It was originally designed around the .32 ACP cartridge, and later expanded to .380 ACP, but when chambered for that cartridge there were some problems.
As for 9mm., first of all the round is too long to fit in the magazine, and to cycle through the action. Second (and more important) the pistol is straight-blowback and the slide and barrel are never locked together, as is the case with most popular 9mm pistols. In a straight-blowback design the 9mm is much-too-much.
You could of course redesign it to be a locked-breech pistol, but the result would be thicker and larger. That would remove much of the attractiveness that the pistol now offers.
Last but not least, many of the potential buyers would want a double-action trigger pull option and a positive firing pin block or lock, neither which was featured in the 1903 design.
Perhaps you should take a look at Beretta's new Nano...