That’s the most childish thing out of this whole debacle. It is extremely clear that you cannot just change your terms 10 years after a company has been created in order to exclude it. Any judge would throw that case out of the window in 10 seconds.
Though I don’t know how much merit his original post had.
"WP Engine accused Automattic and Mullenweg of not keeping their promises to run WordPress open-source projects without any constraints and giving developers the freedom to build, run, modify and redistribute the software."
What promises? People make and release software using the GPL "copyleft" license because they enjoy doing so. Everybody is free to cease doing that if they no longer enjoy it. If it no longer brings them joy. And if it is costing measurable quants of money for the non-profit .org to provide back-end services to the $100 billion dollar corporation who is profiting from using the core plugins and themes etc.
Perhaps 8% of gross is a bit much, but I don't see them counter offering 1% and a way to work up over time. They were purchased for $250 million in 2018 so they have plenty o' cash. Bad faith wpengine for trying to strip-mine WordPress like that.