This isn't about feature flags, per se, it's about abusing feature flags to cohabitate a production and experimental version of your system.

The problem with this is your experiments are necessarily constrained to what you currently require for production - and you've increased your production management headaches. If you're already in the cloud then there's no need for this, just copy your production deployment to your experimental deployment and experiment away. If you're not already in the cloud then here's an opportunity to make you application so it can at least be "lift and shift" into the cloud and run your experiments there. What I wouldn't do is abuse feature flags for implementing an experimental system!