Google announced the ability to create interactive emails using an HTML framework known as AMPHTML (not to be confused with AMPscript). Here is some documentation if anyone is interested in learning more: AMPHTML Docs
I have reached out to Salesforce and they seem to not be able to support this out of content builder at the moment. I was wondering if anyone has found a viable workaround to be able to send these emails through our SFMC IP address and email domains. I was thinking about creating a custom activity route but seems very robust for just sending an HTML file!