Well, if you want an updated 1911, you get a USP-45. Similar in overall size (though slightly more chunky) and operation. Frame mounted safety on some variants lets you carry it cocked and locked and depending on the variant, you can carry it hammer down as well. Polygonal rifling is far better than standard rifling (US military hasn't shot cast bullets for about 100 years so that's a moot point) and the recoil reduction system not only helps reduce the recoil but being it's own built-in buffer, extends service life as well. VERY accurate and stone reliable as well as having an ambidextrious magazine release and with the addition of a new lever, can have ambidextrious safety levers as well. It's also a modular design that allows them to be set up for a variety of modes from SA to DAO to DA/SA selective carry to conventional DA deisgns and for both right and left handed shooters.
Yeah, Sigs are alright for some folks (except for left handed folks that have trouble working the decocking lever) and those that are used to the normal control placement of safeties and slide releases rather that being positioned backwards.
Yeah, Glocks are alright but with no manual safety, I don't see them being adopted by the US military.
I don't think the SOCOM pistol is going to be considered either due to it's massive size and weight. It was a good excersize in designing a pistol to do a job a pistol was never intended to do.
CZ-97 are a maybe since they also have a frame mounted safety but I just don't think that they are going to be given a fair shake in the US military system having been made in a former Communist country. Too many hard feelings and mistrust still remain.
1911 clones are a maybe as well. They're a proven design and armorers know how to work on them so it wouldn't surprise me if they go that route. Great guns but if John Browning was alive today, he would have made the 1911, then the P-35 then the H&K USP.