In Bug 1173407 we added a "first_seen_at" property to tokenserver user records, for the purpose of tracking user-retention behaviour. Unfortunately it was a bit of a hack-job and it doesn't persist across node-reassignments - if we reassign a user's node, they appear to be a completely new user. It seems to have been useful so let's do the work of tracking it properly so that it persists across node-reassignments.
I suspect we won't need to persist this explicitly given the new redshift-based metrics stuff :dcoates is working on; ni? Danny to close if it doesn't sound valuable going forward.
I agree. With the (hashed) fxa uid flowing through to the token and storage servers we'll have all the info we need.