Personally I hope the Lynx wins because it has the capacity to carry 8 in back versus 6 on the other contenders. Ideally the US Army would get an IFV with room for 9 dismounts. I must admit I am a bit disappointed that of the current contenders there are no new American designs. The General Dynamics entry is a relative of the ASCOD like the UK's new Ajax.
The 50mm caliber the Army currently has a preference for is actually just a "necked-out" or "straight-walled" variation of the NATO 35x228mm so the ammunition is not as large as you might think, smaller than ammunition for the 40mm Bofors for example.
I am not opposed to an IFV approximately the weight of and sharing common components with an MBT but that MBT should be something newer than the current M1 Abrams. The M1 remains a capable system thanks to upgrades but there is significant room for improvement with a major upgrade or a new MBT. However commonality would only go so far, the IFV should have the engine in front while keeping it in back is preferable for the MBT.
For weapons the current autocannons being considered (all variations of the Bushmaster series chain guns) are good designs but I think the Army should put a bit more thought into adopting a design like the 40mm CTA the UK is going with. Oddly enough that weapon owes a lot of its existence to US Army interest in the concept back in the late '80s and '90s. I think an ATGM launcher should also be a requirement. Ideally you could have a "dual-purpose" launcher capable of firing something like CKEM for anti-armor work as well as a more versatile missile like the old TOW series.
As for a scout vehicle I'm not certain something as large as the M3 Bradley is necessarily the best fit. Considering the wide range of vehicles the Army used for the role during the Cold War (Jeeps, M114, M551, M3, HMMWV) I'd be interested in learning what they are currently looking for in a scout vehicle.