It will certainly cause confusion because new customer can't get what they pay for regardless bottleneck came from which site. Installer show the speed test result after installation, done deal. Customer service has to handle all the complaints later. Most users aren't tech savvy.

Existing customers should be pleased because it's still a upgrade regardless of 200Mbps (x2 speed from 100Mbps) or 500Mbps (x5 speed from 100Mbps). If they don't have the devices to fully utilities the speed, they can opt to downgrade and save some money. It will be a different case for new user who want 1Gbps and only get 800 or less.