That's interesting, because while I think keto is great in a lot of ways, I've never felt my best on it. It just doesn't give me the energy I need to be effective in the gym.
What I've discovered doing 72 hour fasts is that what I eat when I refeed matters a lot less than when I'm eating throughout the day. Keto made a big difference in my initial weight loss journey, but I find it to be somewhat miserable for maintenance. Yet, with fasting at least 48 hours, I discovered that the macro composition matters a lot less in relation to ketosis. In my eating window, I can eat rice, fruit, etc., and it will knock me out of ketosis for a short while but I'll usually be right back in ketosis between 24 and 48 hours from then. I feel much better in general getting a small amount of calories in, and it hasn't significantly effected my weight loss. In fact, when I was sick a few weeks ago, I stopped fasting and basically ate berries all week. The following week, I went back into a 72 hour fasting routine and still managed to lose a few pounds from where I was at before I got sick.
Put simply, I think the longer a fast is, the less that the need for keto matters. Keto combined with IF can work for a lot of people, and in a lot of ways they are complimentary in their benefits, but people can also tip the balance in favor of either more keto or more fasting and find their own combination that achieves their goals.