I use WP Rocket; it has these features. They’re among the most problematic optimizations. Async loading the CSS just makes the site look terrible under every circumstance I’ve tested. Pages load unstyled, and then pop into the proper formatting later. I’d consider this a specialty feature that would be useful in rare cases.
Async loading the js works sometimes but can cause a lot of problems. I got it to work with the help of Rocket’s tech support (who are amazing). They basically went in, diagnosed the problems, and added specific files and pages to the blacklist for that feature.
Which is to say, if you’re going to have these async features, it’s probably imperative to have a way to blacklist specific files and pages, and it’s helpful to have excellent hands-on support.
Bigger picture, I think if Cloudways wants to make Breeze a hit, they should concentrate on copying everything Rocket is already doing. And then maybe they can push past Rocket, by adding controls over the different Cloudways caching layers (Redis, PHP-FPM, Memcahed, etc.), and by directly supporting server push in HTML/2.