Ha! I calculated the monthly cost as $.9/hr x 730 hrs => $657. You said $648, so that left $9. Sorry for the confusion!
But yes, we already have the per-op model for Cloud Datastore (and it's part of what makes it so attractive!) so you can understand that we're naturally inclined to do just what you're saying. Making Spanner multitenant in a secure, performant manner is real work. But it's what Datastore, Big Query and our other shared services do. I hope you can appreciate that getting "Dedicated Spanner" out the door was the right first step though.
But yes, we already have the per-op model for Cloud Datastore (and it's part of what makes it so attractive!) so you can understand that we're naturally inclined to do just what you're saying. Making Spanner multitenant in a secure, performant manner is real work. But it's what Datastore, Big Query and our other shared services do. I hope you can appreciate that getting "Dedicated Spanner" out the door was the right first step though.