Earlier quoted context omitted.
The control I listed, NIST 800-53 SC-7(7) [which is a part of the FedRAMP Moderate suite of controls], specifically requires you implement a technical control such that your users cannot split tunnel.
Apologies... didn't read into the NIST requirement. Out of curiosity, what do you normally implement that meets that requirement? Forcing all traffic when there is no security benefit (what is the advantage of getting to https://news.ycombinator.com through the VPN?) seems ripe for a compensating control.
The PC you use with the VPN is never to be directly connected to the internet. It connects to a piece of dedicated VPN hardware. (could be a Raspberry PI with special software or something far more expensive) That PC can use the VPN, and thus get to various computers within the company, but it can't go elsewhere. No other business is reachable.
The company can allocate IP addresses without NAT and without regard for the rest of the world. There just isn't any connection to the rest of the world, so conflicts can't happen.