If Mr. Scott were charged, undoubtedly a judge would be brought in from outside San Mateo County to officiate the trial. The ethical conflict of a San Mateo County judge officiating over Judge Scott's trial pales in comparison to the ethical conflict the San Mateo district attorney has in this circumstance.
For example, as one poster pointed out in the other thread, Wagstaffe might have a proclivity not to charge Scott in order to curry favor with a judge who routinely presides over criminal trials that impacts Wagstaffe's conviction rate.
An opposite example would be one in which Judge Scott were charged, but exonerated by a jury. He might then harbor natural animosity toward the San Mateo County district attorney for charging him, and this might impact the people's ability to have justice served in his courtroom.
These are just two examples that make the ethical conflict obvious.
The correct ethical decision is for Mr. Wagstaffe to recuse himself. There is really no gray area here, ethically speaking. Why this hasn't happened yet is very puzzling.