The function of Smart Lock I would like to see (beside not having to swipe the screen when lock is disabled) would be to allow it to be disabled when connected to WiFi networks the user sets eg home WiFi. I find the location variant doesn't work for me as I really don't want location on all of the time to satisfy this feature whereas connecting to my home WiFi should be easy to recognise and thus disable the lock.
IIRC Google is not going to implement this: The official reason is that WIFI SSID's are easily spoofed, the real reason is probably that Google rather has you turn on location services for smart lock so they always know where you are - which is of course part of the business model of Google.
That is all very true of course but the reality is that someone would need to know what SSIDs and/or MAC address disable the screen lock and if this information were protected to the same presumably satisfactory level that what locations are needed to turn it off then surely that argument disappears in a puff of logic?