SmartKey is a mechanical lock that is rekeyable without removing the cylinder. You unlock with the old key, insert a tool to release the internal wafers, then insert the new key and it repositions the wafers to match the key.
oh right! Yeah it's pretty neat actually (for anyone interested[1]). Unfortunately, it does require physical presence/labor (i.e. $$$) by whoever has the master reset tool. For Airbnb's or even self-tours, that's kind of a non-starter.
When you perform a move out or move in inspection, you change the key. It's super easy. The reset tool can fit in your wallet or glove compartment. It's a big change versus having to change the cylinder as in the past. Having to manage a load of electronic locks is likely more costly. Again, this is long-term rentals not short-term.
As for self-tours, they make electronic lockboxes. They've been around forever and used by every MLS.
I'm not going to try to convince you that key-exchanges are bad for short-lived visits (whether electronic lockboxes or not). We just know from experience doing millions of these for a large company that this is very problematic at times and you're better off with a remote controlled solutions that doesn't involve anyone having any physical key.
