This ain't 1990 no more, and most 1-4s are not so crazy atypical appraisal situations that only a local can understand the appraisal problem and perform competently. In terms of how much "geographic competency" it takes to perform an appraisal on a typical 1-4 property I daresay having access to the local database is going to be more relevant than whether or not the appraiser has ever driven through that particular subdivision or shopped at the local Krogers. That, and spending the requisite amount of time/effort to research and analyze the local market trends and the subject's market segment.
I'm not local to Marin City, but even from several hundred miles away I can see 100% of all RE transactions across all property types that have occurred there over the last 20 years and I can find the MLS listings for all of the actual SFR sales that were marketed through the MLS. I can find and understand the zoning (which many of the locals don't even do that) , I can find the topo maps and flood zones and I can see from the overheads when the GLA is reported significantly different in the public records than exists onsite. I don't need to be local to do any of that. I just need to have the skills to do it and the willingness to reinvent the wheel to get to that point.
Now the GSE requirement is a little more stringent in that the appraisers certify to having "the knowledge and experience in appraising this type of property in this market area", but exactly how many assignments in a local does it take to effectively meet that requirement? 2x/yr? 1x/yr? 3x in the last 5yrs?
Sorry, but most market segments aren't that special. Not just for SFRs, but across most property types. Other than timber, ag and mining, of course.