Now Laravel has separated routes for API, in Http\Kernel.php we can set "throttle" (which in Lumen we must copy the middleware from the internet), and other features like Passport. Lumen website wasn't updated, on the homepage you can see: "return ['version' => '5.3']" and the documentation design wasn't updated with design from laravel documentation.
Because the site wasn't updated and Laravel implements features that makes Laravel good for API, I don't see any future for Lumen.
In my vision an app would use Lumen for back-end (api.site.com), vuejs for front-end (ww.site.com), call the API from mobile app.
What do you think ?
A year ago that would be my advice! However Laravel itself is growing so fast now and Lumen is not updated (some open issues as well).
I want to advice you to start your next project in Laravel. You can still create two separate projects for the back and frontend. Also Laravel is still really fast, so you won't have a big difference in performance.
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