I think the virtuous cycles described in the post require having muscle mass, not just being thin.

Yup. Empirically, people who lose lots of weight and keep it off have a CONSTANT VIGILANCE mindset going.

This isn't to say that OP's post is untrue, but rather they're underestimating just how badly the odds are stacked against those who are obese.

HBO's The Weight Of The Nation documentary goes into the Weight Control Registry study on long term weight loss, and the common factors between people who manage to keep it off:

https://www.youtube.com/watch?v=hLv0Vsegmoo&t=1h1m28s

One of the points I was trying to make here is the underappreciated importance of path dependence and homeostasis (so a person who has always been thin will have a much easier time than someone who had to get thin).

Sure.

Reading the original study, it seems like one problem is that even though leptin returned to normal, it was out of sync with resting metabolic rate, which meant appetite was no longer linked to energy requirements. There is some suggestion that a slower rate of weight loss might have more success in changing the set point, but that's also contentious.

Not everyone has room at home. I have a barbell, a few dumbbells, a pull-up bar, and my own body weight, and go everywhere on my bicycle, but I also go to the gym because there are exercises I want to do that I can't do at home.

Gyms can also provide training (of variable quality, but everything on the market is of variable quality), and communal activities like Cross-Fit. A gym is a resource to be used.

The guys lifting big weights are seeing to their own business. They are not thinking about you, and you need not think about them, except as an inspiration to become them.

I see a lot of people at the gym much stronger than me, and and a lot much less strong. But we are all doing the same thing: what we can.

Can't find good sources, it mostly seems to be anecdotal based on the ranges that strength athletes choose to stay in. My guess is that if you went too low, you'd know about it (stage-ready bodybuilders are in a world of pain). Also, kudos for maintaining a single digit body fat percentage - impressive!

There are no guidelines on this that I'm aware of, but it seems unlikely that the RDI scales linearly with lean body mass. Some proportion of micronutrient intake goes towards the likes of bones and organs and the brain, which is unchanged by having more muscle mass.

I'm less confident of this than I am of the opposite framing: people with a low caloric intake have to be more careful about eating nutrient-dense food.

There are no negative consequences, because nothing happens in isolation. Obviously there'd be negative consequences if the average person did this, or if Berkhan ate an entire cheesecake every day. I'm not really sure what point you're making here.