Let’s calm down a bit. I could discuss at length about the multiple reasons why the arguments from the mentioned post are wrong, or twisted, or otherwise. Maybe for another time, but for now it is enough to say that it looks like a piece of not well designed PR for gold open access. PR is a profession by itself, it has its techniques and means to achieve the goal, but here the stellar mathematician Gowers just shows that PR is not among his strengths.
Maybe it means that there is a need for public figures to support this shaky construction.
At second thought, the FoM is not the end of the world as we knew it. Is just yet another journal which tries to salvage what it can from the old publication model, who was once essential for the research community, but is now obsolete because the net is here.
The real matter is though not FoM, or Gowers “betrayal”, but the fact that we have to look for new models of publication. Once such a model is found then naturally any FoM will decay to oblivion.
Take for example the business of publication of encyclopedias. Enters Wikipedia, who proved it is scalable and it is sustained by millions of enthusiasts, btw, and now the encyclopedias business is no longer viable. It will happen the same with the publication of research articles.
Better is to try to think about a good model. Consider for example two related ideas, discussed here: