Ryan did mention this in his talk at React Conf. Shopify has had issues adopting Remix because their existing front-end codebases are massive and they couldn't

Ryan did mention this in his talk at React Conf. Shopify has had issues adopting Remix because their existing front-end codebases are massive and they couldn't afford to rewrite them to use Remix. That's actually the whole motivation behind turning Remix into a bundler plugin. With a bundler plugin, you can incrementally migrate parts of your existing application to use the features of Remix without having to rewrite all of it.