Just tried taking mine over for the first time (Model X).. Not a great result...
Maps turn off at the border with the message:
Maps Disabled
Google Maps and Search are not available in China
So even still getting a HK signal maps don't work, I assume it's a limitation based on GPS location.
Roaming doesn't work over the border, just no signal in China at all and doesn't pick up a local network.
Running hotspot on a phone with HK sim enables Spotify, but still no maps.
Not sure what options there are for maps other than wait to see if Google and China can make friends with each other again?