"No usernames" is not useful if you want to create a social media platform. It could be the beginning of a spin-off, something completely different than a social media outlet.

Usernames (or, in broader terms, identities) are necessary for many reasons, if only for personal branding. I, for instance, I would like to be known for a certain type of topics, as an expert, and I would spend time and creativity to build that personal brand in order to leverage it on other places (coaching, consulting).

Anonymous transactions could be an interesting option.

Limited SP to a certain account is something that makes me go "hmmm". But I may be biased, since I come from an ex-communist country, where all people had to be "equal". At the first glance, I would say "no" to that.

Powering down does create some market predictability and opens the door for speculation (I don't think it necessarily pulls the price down, though) and I'm sure the design of this could be refined.

Keep shooting, I'll try to catch your bullets :)