I have pretty significant doubts about both the practically and functionality of adding a vertical grip to a pistol for the purposes of recoil control, especially in the context of concealed carry based on my experience in shooting USPSA. The current philosophy in competition shooting (where a lot of the modern technology and technique originates from) is that you shouldn't have to fight the recoil but instead manage it consistently so that the muzzle is predictably returning to where you want it and you're shooting based on an appropriate cadence for the target and distance. I personally don't think a vertical foregrip would facilitate this, but I'd imagine if the NFA were repealed you'd find some guys in Open division experimenting with it and maybe a new, better grip technique could develop.

On the other hand, in the world of concealed carry, since most popular carry guns are too small to get a proper support hand grip, a small hook either in front of the trigger guard, under the dust cover or just under the trigger guard itself to lock in your support hand index finger, combined with a small gas pedal to index your support hand thumb would probably add a significant amount of control to be able to reduce those splits without being as obtrusive as an actual vertical foregrip.

I think you'd probably be more likely to see incremental advancements and evolution of integrated suppressors / baffle stacks vs. things like fold out stocks or foregrips if the NFA were repealed.