We are writing Version 2 in PHP 7.3 with Laravel. We're pleased with it's performance (our hosted solution operates at large scale using Laravel) and it's our favourite language to work with. We'll be building the frontend in EmberJS and it will be incredibly fast.
Awesome that you're using Ember! I'm hoping that (from my earlier question) I'll be easily able to track of page load/unload events using route transitions if I'm using this product.