I don't think this is complicated... unless you make the mistake of making it complicated.
There is a spec for axial and radial runout limits for the rear wheel. This spec isn't about the bearing, it is about the wheel. If you have ever rebuilt a spoke wheel, you understand this pretty well. WRT to a cast wheel, the spec basically relates to whether the wheel is servicable after damage.
With respect to play at the rear wheel with the wheel properly mounted to the final drive, there should be no play detectable by feel with the hands. Putting a micrometer on this assembly makes no sense.
If there is detectable movememt of the wheel when it is mounted to the final drive, the source of that movement needs to be identified. I could be the final dive, but if it is the final drive, you are likely to be experiencing roughness in the ride, and oil leakage. A more likely source of looseness is the pivot bearing which have a history of developing play. If this is the source of looseness, the bearing should be replaced IMO. I have read many reports of looseness at this point being "fixed" by re-torquing" the pivot bearings. That will eliminate the play for a while, but will fail to identify the original cause of the play which is probably degradation of the pivot bearings (a common finding). Play at the pivot bearing is best repaired by removing the wheel, the final drive, and inspecting the pivot bearings. At this point you can anticipate replacing the pivot bearings.
Another source of play at the rear wheel could be the swing arm mount, but I haven't read reports of this and consider it an unlikely source of play at the rear wheel.
In summary, ANY axial or radial play detectable by hand at the rear wheel is an indication of a problem and the source needs to be identified.
Addendum: In a subsequent post, the term "lash" is used. Just to make sure we are talking about the same thing, all bikes (all vehicles for that matter) have some driveline lash. This is a consequence of spacing and wear between gear teeth.
Axial play, as detected by grabbing the wheel at the 12 and 6, or 3 and 9 o:clock positions and feeling for movement, would not be described as "lash" IMO. This would simply be axial play and the limit is zero detectable by hand. You would be able to measure some with a micrometer, but I don't know that there is a spec ( I don't think so), and the spec would be pretty meaningless since that play would be the sum of several sources.
Quote "My rear drive fears got the best of me prior to my Alaska trip in 06 so I changed the bearing at 48K."
Was the preload for the new bearing checked prior to assembly, or was a new bearing just installed with the original shims?
I am currently rebuilding another final drive that has indications that the drive is on its second failure. Replacing a bearing without checking for preload and just using the original shims is asking for trouble IMO. However, a preemptive rebuild done this way probably has better odds of long term survival than does a rebuild of a failed final drive without doing preload measurement. Again just an opinion.