Well, as of today this wouldn't work because not every hotel uses the same shape mag stripe key. So this would require an infrastructure upgrade, as mentioned above.

The concept of a wireless enabled lock is out there, and is probably the way to go. (Locks talk to local wireless router which talks to door controllers which talk to master computer which is fed your "special key" number.)

And then Marriott can charge $9.95/day for the service, but waive it for GE and PE