Even the bullet points you enumerate early on are arguable for various people. For diabetics, you absolutely want a greater amount of calories from protein and fat - taking in 40% of your calories by carbohydrates is too many for a diabetic's damaged endocrine system to handle. For athletes, the distinction becomes even more complex. What sort of athletes are we talking about? Endurance athletes, like marathon runners? Pure power athletes, like olympic weight lifters? Or some sort of mix of the two, like baseball or rugby players? I cannot imagine a weight lifter trying to source 40% of their energy off carbohydrates - there's just no way they'd take in enough raw material to replace the massive damage their training regimen does to their muscles.
We also need to be clear on the type of fiber we're talking about. Digestible fiber comes from your wheat breads, your all-bran, etc. This fiber can be broken down by your system, but will generally not provide you a huge amount of nutritional benefit. It is mostly used for working out the 'net carbs' in a food by subtracting them from the overall carb count. Indigestible fiber comes mostly from vegetables, and some fruits like apples. This is the fiber that helps seal and slick your gut to make digestion of everything else much easier.
Digestible fiber is very useful for cutting regimens and helps maintain a good gut flora environment, but generally people get plenty of it and it's not a concern. Proper consumption of indigestible fiber relates directly to overall digestive health, so it's basically always a concern.
The reason, I think, you did not find an upper limit is that most of the theoretical problems from consuming too much fiber basically solve themselves. Overconsuming digestible fiber will mean your body spends too much time breaking down the stuff that doesn't provide it much nutrition. Your body will respond to this by inducing an acute craving for what it requires, and you will not feel satisfied until you satiate it. Overconsuming indigestible fiber could theoretically coat your gut too thickly to absorb micronutrients that your body needs (such as vitamins) from a normal concentration of it. However, the vegetables you'd have to consume to accomplish this are so rich in these micronutrients that you're going to have a much higher concentration in your gut, anyway! Here is a good article with a fiber overview and a decent number of cited sources for further reading if you want it.
As always, for active people the #1 thing is to focus on your macronutrients. Getting worried about things like this is a great way to get off track and miss the forest for the trees. It's a great question, but its overall impact on your physical fitness, particularly with regard to training, is not going to be anywhere near as great as getting the right mix of protein, carbs, and fats in your diet for your training plan.
