Gone from rapid weight loss to plateaued weight loss (POSSI

I've been having lots of conversations with people lately about why they go on a huge calorie deficit (i.e. 1,000kcal or more deficit /day) they experience rapid weight loss (5-6 lbs per week) the first week or two, think it's all fat loss, then their weight loss stalls or the rate of weight loss drops dramatically.
So here's my hypothesis. Take it for what it's worth, just my $0.03 (inflation), I'm not claiming to have the ultimate unrefutable explaination, I'll even admit before hand, I may even be 100% completely wrong. These are just my thoughts.

Say a person cuts their normal caloric intake by 1,000kcal/day and begins exercising and doesn't eat back all their exercise calories, or less than half even. The body uses glucose for energy. Glycogen is stored in muscles and the liver, it is broken down into glucose when it's needed. The body can store roughly 500 grams or 1 lbs of glycogen. Glycogen is stored and bound to water. Some literature says 1 g glycogen binds to 3 g water, some says 4g of water. For this purpose let's just say 3 g of water. So if a person eats at a large 1,000kcal deficit, which will cause the body to tap into the glycogen reserves for energy, and they exercise intensely, which will further tap into glycogen reserves, over a week, the body can easily drop 1 lbs in glycogen reserves, along with it's 3 lbs of water. I say it may take up to week, because if you are eating a relatively high carb diet, you're going to be replenishing some of those reserves, just not at a rate fast enough to replenish them completely because you're eating at a huge deficit. Now if you're eating a low carb diet, you can easily experience a 4 lbs loss in a few days.
So where does the additional rapid weight loss come from you may ask. Muscle is also used as an energy source, usually about 5% of total energy used comes from muslce and the % can go up with intense exercise. During INTENSE exercise (above fat burning zone), protein will become the primary energy source, it is converted into glucose by the liver. Fat is the prefered energy source at roughly 50% of your max heart rate. Granted you will burn more total calories with Intense training vs moderate fat burning zone training. With such a large caloric deficit in such a small time, glycogen reserves won't get replenished so the body will continue to use muscle for a greater than normal percentage as an energy source. So, if your glycogen reserves are depleted, you will be using primarily muscle and some fat for energy during intense training. Remeber, 1 gram of muscle is bound to roughly 4 grams of water, so the more muscle you break down for energy, the more water weight you will lose.
Say you maintain this huge caloric deficit and intense exercise routine for a few weeks and experience rapid weight loss. Soon you've lost several pounds of muscle along with some fat, your body will realizes it's not getting adequate macros to replenish glycogen reserves. A reduced metabolism is the result of the huge decreased caloric intake and muscle loss. Your body's metabolism will slow down in order to adjust to the huge caloric deficit and the muscle loss will lead to less calories burned. Which will lead to the proverbial plateau even though you're eating what you thought was a deficit, it has now become your maintenance since you've lost calorie burning muscle and your metabolism has slown down dramatically.
How do I avoid this from occuring then, you're most likely asking by now.
Reduce you're caloric intake slowly, roughly 15% below TDEE, so that you minimize or even prevent the decrease in metabolism. Give you body time to slowly adjust to the calorie deficit so your metabolism doesn't crash rapidly. A nutrition professor once told me, "most people's metabolism decrease, is as dramatic as it's caloric intake decrease". So, also eat plenty of protein to decrease a catabolic state and weight train to minimize muscle loss. Carbs aren't bad. If you do come to a plateau, which shouldn't come quickly, either reduce caloric intake slightly or increase your exercise duration or intensity.
I'm sure someone out there has more knowledge on this subject and will have some corrections for me, please speak up. I've got tough skin and don't mind being schooled.