I saw the name "Dr. Stephen Phinney" pop-up in my search in these forums regarding this topic. Last night I watched a video presentation of his regarding research on a low carb diet and endurance exercise (of which there doesn't appear to be much research in this area). One takeaway from the video that aligned with my experience in eating a low carb diet is that
it takes time before one experiences the benefits. One can't go low carb for a week or two and expect good results; a short attempt at adapting your body to fats as the primary fuel source will likely resulting in significantly decreased performance. It's my opinion that this is why so many people don't think a low carb, high fat diet is compatible with intense exercise as few people are willing to 'pause' their cycling career for months or even a year to allow their body to adapt.
Apparently a low-carb diet works well for ultra-endurance athletes as one doesn't need to be eating all the time to replenish glucose. While I'm no ultra-endurance athlete, not needing to eat on riders between 40 and 80 miles is definitely something I've never been able to do before without bonking hard.