Why do you (editor) assume that the county would be "obliged to mount what would almost certainly be a long-shot legal defense."  The voters preform a legislative function when voting on initiative measures, but the county still has an administrative role to play, or not play as the case may be.  The county could reasonably chose to not enforce a law it determines to be illegal in substance or unconstitutional.  Measure proponents could conceivably file a mandamus action requesting a judge order the county to enforce its code or charter, but the defense would be fairly simple.  It is also possible that the county could refuse to put a measure on the ballot that doesn't comply with ORS 203.725.  Challenges will always be part of this process, but I don't think the county would be faced with a "long-shot legal defense."