Have you seen how images load in popular apps such as WhatsApp, Instagram, or on Medium's website? This technique is called "progressive image loading" or "the blur up technique" and it's actually not hard to accomplish on HubSpot's COS thanks to it's auto image resizing capabilities.
I wrote a blog post on how to do it, but in short, all you have to do is add a URL parameter to the end of an IMG's src attribute "?width=20" and then you can fade it out once the full size image loads with some javascript. For more details on how to implement this with full width background images, read my blog post.
I'd love to see other ways this can be used or if anyone has tried anything like this in HubSpot.