I'm generally supportive of this Constitution idea, but I have a few concerns/thoughts:

As I see it, there are two main reasons to have a Constitution. First, it helps create a culture or a "tribe" of people who share similar ideals, at least in certain limited respects. By requiring each person to "sign" the Constitution before opening an account (can this actually be built into Steem?) we are, essentially, self-selecting the type of people that we want here to a limited degree. That's probably a good thing provided that the tent is sufficiently large to ensure Steem's continued growth.

Second, a Constitution serves as a bit of a "check" on the power of stakeholders. Though (as noted by a previous commenter) stakeholders are not technically bound by the Constitution (in the sense that 51% of the stake has the power to do what it wants), adopting it could serve as a very real deterrent to them using this power in a way that violates the Constitution. Here's why:

The ultimate "check" on the power of the 51% is the markets. It's the market price of the token that actually secures the blockchain. Higher prices equal more security, and vice versa. Stakeholders are incentivized in numerous ways to maximize token value. If all holders have signed the Constitution (meaning, presumably, they that support its principles) and then 51% of them act in violation of those principles, the minority may "opt out" by dumping their state, thereby decreasing token value and punishing the 51%. Thus, the 51% is only likely to violate the Constitution when, in their judgement, there is overwhelming consensus among stakeholders to do so or when the importance of doing so is, in their mind, worth the cost (that is, the decline in market value).

Regardless, I do think that having a Constitution serves as a useful check on the power of the majority.

I'm a little concerned about invoking law and jurisdiction, however. That seems to be a slippery slope. Blockchains are currently (and arguably) a law unto themselves. This is due in large part to the fact that it's virtually impossible for any single court to gain sufficient jurisdiction over a majority of stakeholders/miners to compel them to act or forbear. By invoking law and consenting to jurisdiction, we may be opening Pandora's box. I would think long and hard before including any reference to sovereign laws or jurisdictions in the Constitution, or even mediation/arbitration.

Regarding the specifics of the proposal, here are my thoughts:

A) Do paragraphs 1 and 5 not conflict? 1 suggests that transactions will never be reversed and 5 implies that they can be in order to honor intent when the issue is large enough. This needs clarified.

B) In paragraph 5, I’d suggest setting aside some fixed percentage of the new Steem created with each block as a bug bounty escrow and/or insurance fund to reimburse those who are harmed by bugs when the community agrees to do so.

A concern that I don’t know how to remedy is the perception that reimbursement of losses is more likely to be approved when large stakeholders are harmed by the bug than small ones. This has been an issue of fierce contention in Ethereum (the perception that Ethereum whales are lobbying for a hard fork only because they personally suffered major losses). This issue needs some thought because it could easily divide the tribe.