"Must be fully operational as described in the brochure without an internet connection. Any features that require an internet connection must be priced and sold as optional enhancements."

Done.

Rather than regulating features, I'd start with a dependency list.

So a smart plug might have a list saying:

- Functionality requires 2.4GHz WiFi, Internet access, access to whatever.vendor.com, and a vendor.com account.

- Provisioning requires the above plus BLE and Vendor's app.

A smart washing machine might be more complex:

- Express wash requires nothing special.

- Regular wash requires 2.4GHz WiFi, Internet access, access to whatever.vendor.com, and a vendor.com account.

- Heavy Duty wash requires the above plus a vendor-supplied detergent cartridge.