Blood sugar levels are not something that needs to be babysat by a metabolically healthy person. We should be able to seamlessly move from being fueled by glucose to ketones. (Well, I suppose suddenly running out of available glucose because of strenuous endurance activity can sometimes be rough waiting for the switch to complete. Thing is, once in ketosis this kind of activity is
easier as energy supply becomes more steady state)
The only broad concern I would have is being more prone to accidentally having too much calorie restriction for a prolonged period, where metabolism reduction, potential thyroid issues, and potential nutrient deficiencies can come into play based on highly individual thresholds.
I also suppose some people who fast, especially on very low carb/carnivore diets can sometimes experience the exact opposite of your concern, their blood sugar levels can become constantly elevated, seemingly induced primarily by elevated cortisol, though also seemingly effected by other complicated individual factors like the kinds of stored fatty acids they are burning.