Not really sure the section you mean.If you mean inside the hub at the bottom of the arrow you can't do much if it is worn .If it was machined the planet gear housing would hang out the other side.
Only option if it is bad is to cut for a roller bearing in that position
If you are reusing the planetary make damn sure the bearings are good and that the gears turn freely. A hub with that much wear is not rare by any means but it does indicate that the fluid was NEVER changed and the rest of the bearing surfaces saw that same fluid . You can machine it for a roller bearing set and make it a rollerized transmission or just replace the hub but it will be difficult to use it as is when setting clearances and the new thrust bearing will wear improperly.
the gears seems to spin fine. The guy I got if from had rebuilt not that long ago. But it lost reverse and he thought the lower planetary gear broke. I don't remember what it was behind but it was a heavy, 4k, car. But both the gear sets spin fine. Is there a more accurate way to check them than just by spinning them?