It made it by default. It's also not much of an "opt-out". An opt-out would be called "disableStreamingMetadata". Names convey intent, and it's obvious this is intended to be the behavior for all users with maybe an exception.

The problem is that this is needed for a minuscule amount of users. This should've been an opt-in. The choice to make it opt-out is quite weird.

make sense now. They should add disableStreamingMetadata option to completely disable it instead of disabling it by matching user agent in a irreverent field name.

Many people choose Next.js because it has better SEO support than other options.