This is unenforcable because most establishments aren't going to harass customers and turn away business because of some bullshit "reasonable rule". Our consumer rights haven't been eroded to that extent.
The comparison with smoking doesn't fly because smoking indoors in public is illegal and a health risk.
I'm not comparing use of tablets to smoking. I agree that they may end up having to call the police if you won't leave when asked to do so. They decide who they will allow in their place, and as long as they're not discriminating against you unlawfully you have to leave when asked.