I agree it's the biggest risk.

If someone can ask the question in such a way as to make themselves known to be a sysadmin, then who the end-user is should not matter.

But if it's naive end-user questions (who happen to be the sysadmin for their home systems), serverfault will fail.

I don't think the requirements should so much be "in a professional capacity" and "other than your own" so mcuh as it should be that it is -indistinguishable- from a question asked in a professional capacity.