I fear that 80% may be too high of a threshold for amending the governance system. I don’t have hard evidence for this, but my sense is that even a 2/3s voting threshold is very hard to achieve (it may not be hard to achieve in small groups or groups which are very collegial, but my sense is that it is hard to achieve in large groups which have polarized factions, which i believe is very common in large groups).
What supermajority thresholds do groups tend to use (for amendments but also for other supermajority thresholds)? The most common choice seems to be 2/3 (a little over 66%), which is found in, for example, Robert’s Rules, the US Constitution (although 2/3s is used for some things, US constitutional amendments must be ratified by 3/4 of the states), the German Basic Law, and elections in the Catholic Church. The next most common choice seems to be 3/5, which is found in, for example, the US Senate, the UN Security Countil, the South Korean National Assembly, the EU Commission.
A simple majority of shareholders can amend US Delaware corporations; in the UK and Germany, the threshold is 3/4 (in some cases these may be defaults that can themselves be modified by amendments) (Section 242(b)(i) of Delaware General Corporation Law ; UK Companies Act 2006 Sections 21 and 283 http://www.legislation.gov.uk/ukpga/2006/46/section/283 ; German Stock Corporation Act (Aktiengesetz) Section 179 http://www.nortonrosefulbright.com/files/german-stock-corporation-act-147035.pdf).
Thresholds higher than 3/4 are so hard to meet that they are sometimes regarded as forms of approximate consensus.
For example, the Occupy Cincinnati group used a 90% threshold for ordinary decisions, and this was said to render making decisions “pretty much impossible” (Justin Jeffre, quoted in The Occupy Movement and the Poetics of the Oppressed by Ursula McTaggart), and some experienced activists believed that high supermajority thresholds led to the Occupy Cincinnati movement’s downfall (ibid).
The difference between 80% and 75%, or between 75% and 66.66…%, doesn’t seem so great, but the difficulty of meeting a high threshold is probably superlinear, for the similar reasons to the reasons that improving a web server from 99.9999% uptime to 99.99999% uptime is probably harder than getting it from 60% uptime to 61% uptime.
66.66…% (2/3s) may not sound high, but consider that if the threshold is 2/3s, then you are saying that we won’t amend until there are at least two people who want to amend for every one person who prefers the status quo.
Similarly, 75% (3/4th) is saying that we won’t amend until there are at least 3 people who want to amend for every 1 defender of the status quo, and 80% is saying that we demand 4 amendment supporters for every 1 status quo supporter. Seen in this light, an 80% threshold sounds like quite a lot. If there are three people who like an amendment for every one person who dislikes it, then do we really want to allow that one person to block the will of the other three?
I recommend a threshold of 2/3s.