Okay. 3 schemes I see that would do this.
- BAE/Nexter 40mm CTA The French and British have been integrating these in there new vehicles. The 40mm has lots of ammo and punch the shell is a 40x255mm in a 65x220mm cartridge . Coupled with an anti tank missile launcher like the javelin. A 7.62x51mm coax and possibly a 12.7mm in remote station.
- Northrop Grumman Bushmaster IV 40x365mm this is the same ammo as the Naval Bufors L70 sometimes called the Mk4 40mm it's also the same as used in the CV9040 And K21. It's a big older round that still packs a punch. 7.62x51mm coax, anti tank missile launcher and possible secondary remote weapon in the .50 BMG
- Northrop Grumman Bushmaster III 50mm conversion. A variation was shown at AUSA 2018. The Bushmaster III is normally a 35x228mm gun this round is in common with a number of naval 35mm cannons and the German Rheinmetall Lynx that have been displayed. however back in the 1980s and early 1990s developers realized that the cartridge case is actually 50mm not 35mm and they could neck out the round to this wider diameter and load a semi telescoped 50mm shell. This became the 50x330mm Supershot. The round was roughly the same size as the 35mm packed the propellant capacity of a 40mm Bufors and a lot of punch but it fell out of favor and no one adopted it. Years later the U.S.Army started looking at it again for potential anti artillery use in the form of the 50mm EAPS Extended Area Protection System which seems to lead us to the GDLS Griffin III. It's still a big round limiting potential magazine capacity but it would do a number on enemy armor. Early concepts for the MPF infact had 50mm weapons instead of 105mm tank guns. Partner with ATGMs 7.62 coax and .50 RWS and it would do nasty things to BMPs.
- There is a 4th option which has a back story like the 50mm. The Northrop Grumman Bushmaster II 40mm. Again back in the 1980s developers were looking to squeeze big rounds in little packages the 30x173mm casing is actually 40mm in diameter so they necked that out and created the 40x180mm Supershot with a powder load equal to a 35mm round. Again more punch smaller package. The Bushmaster II its based on is the is the same as already on the Stryker Dragoon Ghost rider gunship and Zimwalt class destroyers.
In #2 the U.S. DOD never really adopted the 40mm L70 Bofors round and I don't see a reason to now. In the case of number 4, the advantage is there of being able to convert from existing guns but 40mm Supershot never went anywhere and even if you wanted to why bother, other than to use existing guns there is no advantage vs Bufors or 40CTAI.
I like the 50mm Cannon I do and if this were a USAF gunship like the Ghost rider or a upgrade to the Zimwalt class I would say go for it. The problem I have for a IFV is ammo. You need a nice easy to store package the 40ctai does that for an IFV not so much the 50mm.