You cannot use a .dev domain/subdomain on Remixer Cloud Hosting since it does not support HTTPS/SSL certificates. This applies to situations when you publish Remixer Cloud hosted sites using the Publish button (not the Export to WP button feature, which exports to DreamHost's shared WordPress hosting).
The following describes the .dev domain, and how HTTPS is forced by default.
What can I find more information on .dev domains?
The .dev domain is owned by Google. As part of Google's initiative to secure website connections, .dev domains force HTTPS be default. You can see this is mentioned when originally purchasing the domain registration:
Please note that since HTTPS is forced at the registry level by Google, there is no way to override this redirect. The only option is to install an SSL certificate to ensure your site does not throw a browser warning.