the 9mm Parabellum is NATO standard since 1962, not bloody likely they'll change. Simpler logistics when SMGs and pistols can all use the same ammo.
The possible canidates that could threaten 9mm standard would be:
.224 Boz: A subcaliber based off 10mm, it would have the penetration of a subcaliber, commonality with other .223 caliber barrels. One interesting feature might be the possibility of using a wide variety of civilian ammunition (sounds good for behind enemy lines commando stuff) by being converted to use 10mm Norma, .40Auto, or .357SIG ammunition.
http://www.civil-defence.org/products/ballistics/boz224/boz224.html
5.7x28mm: Fabrique Nationale's subcaliber which has already shown good use in both an SMG and pistol. It was actually created with asperations of becoming NATO standard
http://www.remtek.com/arms/fn/p90/data/concept.htm . The HK competitor 4.6x30mm won't win just because they're both so similar (ok, the HK has slightly more penetration but the FN has slightly better pentration) but the FN cartridge was created earlier, is more popular and already proven in two weapon systems.
6.5x25mm: created by Saab-Bofors, it's a subcaliber conversion to 9mm Parabellum. Not much is known but there was an interesting article about PDWs in the October 2000 issue of Guns and Weapons for Law Enforcement in which this cartridge was mentioned. This would be the most economical way of getting better capabilities in a sidearm or SMG and in my opinion the way the US and NATO should follow. In my opinion the M9 is a fine weapon that will last many years and if they do modest upgrades (like they did with the M16 becoming the M4) by changing to this subcaliber and possibily replacing aluminum frames as they wear out with titanium frames (I'm crossing my fingers hoping that Beretta is moving in this direction with the Tomcat Titanium) the M9 will last even longer.
Both the p226 and the 92fs won, the 92fs was just a bit less expensive. they still like the sig enough to adopt the p228 but the weakness of 92FS slides has been an issue and SIG slides (mostly before the 229) are weaker than the 92FS's
I like the second strike requirement in how the US military defined double action. You can't always depend on the quality of your ammunition Glocks and Berettas are both very reliable, the Glock is extremely durable and the Beretta is reliable even with very low quality ammunition (strengths and weaknesses).
