I gave that letter a couple reads this morning and I have to say I'm pretty conflicted over it. On the one hand it does say some things that needed to be said. On the other hand it doesn't even touch on most of what I think is important here.
I am aware that my resignation was a bit of an outlier¹ as far as what core issues it was based on. The bulk of the outrage was focused much more on how the specific situation was handled rather than why it happened at all. The letter addresses almost exclusively the fallout, not the underlying problem that I believe led them to this point.
If I do sign, it will be almost exclusively in support of Monica's situation in particular and against the public defamation she experienced in being ⓐ accused in a way that implicated her of having done something far more serious (and even categorically different) than she actually did and ⓑ that claim being reiterated to the news and elsewhere.
If I do not sign, it will be because it leaves the door wide open for SE to just paper over the whole situation with a few apologies and bit of position shuffling. Although it mentions giving moderators agency again, nowhere does it even hint at the issue issue some of us had with the Code of Conduct changes (namely the positive rather than negative form of edict) nor is there any call for the company to stop using its platform to promote a specific side of moral, religious, and political issue(s). In a very real sense using their company as an advocacy platform rather than sticking strictly to doing business has tried to trade on the good name of the many people who have contributed, many of whom do not agree with the stances they are taking.
Even if everything in that letter is addressed and 95% of the resigned moderators pick up their shovels again, the underlying cause will not have been addressed. The issue of diversity as it relates to this site will not have been addressed. If holding and carefully articulating a point of view can be considered offensive just because the other party says it is then this site is doomed to never host more than dim echos of what its constituents actually believe.
It will be easy for outside readers from the rest of the network to write this off as a lame excuse for allowing bigotry. Yet if you read what I've written and advocated for here I think my 8 year tenure as moderator here is evidence to the contrary. Look around meta and see all the flack I took for not allowing this to be an 'anything goes' venue. I deleted 2.6k posts and 8.3k comments as a moderator. I deleted lots of things about viewpoints other than my own that I believe were true, they were just inappropriately said or placed. I adamantly defended other groups' right to use this space to criticize the beliefs I hold.
Until Stack Exchange either decides to avoid using their corporate agency to back specific causes entirely or realizes their error and openly advocates for a different definition of diversity than the one they are using (i.e. "the assortment of people who all agree with premise X" is not diversity and "all meaning is exclusively in the eye of the beholder" is not inclusivity.), I still think they have neutered the platform's ability to operate in this space.
¹ It wasn't unique though. Nathaniel, Gilles, Robert (reasons), and others' resignations, those that reference them, and a host of comments echo similar concerns. Does this represent a majority view? Not even close. All I'm saying is that I have not been entirely alone in these observations.