This feature was added at some point to Nuxt 2 and is currently only being supported for opt-in webpack builder.

Following Nuxt default behavior, supporting external config files is an anti-pattern. We use a unified nuxt.config to configure all of the integrations including vite, webpack, typescript, and other libraries. This unified system makes Nuxt behavior more predictable as we have once a source of trust and modules integration to extend the config simpler.

Other notes: Discussing with @danielroe, supporting an external postcss config, makes option extending by modules more limited. Any changes they make to nuxt.options.postcss will be dropped in case of an external config and they need to rely on extend:postcss. This is a negative DX considering modules are able (and typically do!) to extend nuxt.options. We can load it in schema level as a workaround but that also makes schema more complex and likely to have inter version compatibilities.