At this point, it's not even about the action against WPEngine anymore. Automattic/Wordpress hijacked ACF, one of the most popular community plugin, and then threatened other independent plugin creators. So Matt's willingness to continue escalating makes me too nervous to build anything new right now.

If you self-host Wordpress, and not rely on the built-in plugin library, you are probably safe. But now you are apparently responsible to do your due diligence to make sure any service you use is either a) is safely independent of WordPress's services or b) paying Automattic/WordPress royalties.