Hi @marianberry , I’m sorry this has been costly for your clients 
@Joe_list Of course you can use any element you want to in HTML -- but here we’re talking about people being unable to use the email tool in HubSpot to automatically pull in their featured blog image from WordPress (or similar). It’s precisely because you can use whatever HTML you want to that we can’t pull in the image reliably. For the email tool to be able to do that, you can’t have the featured image element named whatever you want - the tool won’t know what to look for. That’s why it does actually need to be part of the RSS standard in order for us to include it, because as it is (not part of the standard), there’s no way to reliably pull in the featured image from blogs hosted outside of HubSpot.
For anyone looking for a solution, I’ve heard customers have had success with this WordPress plugin.