If we think logically then it might not seem harmful to combine the two diets as keto is all about restricting the food intake and in intermittent one has to restrict the time interval. They do not overlap in any case.
But as per experts it might not be a good idea. First of all, keto is a restrictive diet, which means the body is already missing out on necessary nutrients. Pairing it with intermittent fasting might put more stress on your body, which might have great repercussions. The overwhelming experience might lead to mood swings, irritability and fatigue.
Also, as per some research, weight loss due to keto stays for a short term. But maintaining the diet can have a positive impact on weight, triglycerides, and blood glucose level.
Combining keto with Intermittent might work for some and might not for others. It might be more harmful to pregnant women and people suffering from chronic disease.