Until it actually passes into law - who knows exactly how it would work.
I wouldn't use it as a selling tool, but if the customer is asking to get quoted on the swap. I wouldn't try to dismiss it.

To me -this will be a Federal managed program. Electricity running into a building can easily be monitored by the meter.

I don't see any easy way to control the use of propane- it's not like it's plumbed into each company. All a person would have to do is have multiple venders.

But I wouldn't want to guess on anything until the law is actually put into effect.
I think your customer is just trying to use common sense.