If you really feel the urge in getting second kemper i would go 1 rack/head and second one is stage, this way you can control the head with the stage as remote and keep it for live usage.
As about stereo rig, idk guys if you are the only guitarist in a band then 2 amps are almost essential. Look at the bands like Royal Blood where Mike Kerr sends his bass into 2 amps (1 pitch shifted up to imitate guitar) and it works great. Also guys like Adam Jones blending 3 amps to get that really thicc guitar sound. If you can afford/pull it off its great i think. Also doing stereo rig is cheaper than having another mouth to pay/feed in a band :). Definitely not for everyone though since you have to change the way songs are written/mixed among many other things.