The RSS feed is still useful! For example, if you are using MailChimp to send your latest posts, you'll have to do it via RSS, so it would be a good idea to also enable the featured images there to improve the aspect of your newsletter.
To enable your featured images in your WordPress RSS feed, you need to do the following:
1. Go to Plugins - Add New.
2. Install and activate the 'Featured Images in RSS & Mailchimp Email' plugin.
3. Then go to 'Featured Images in RSS Feeds' and choose the size and alignment of the images, as well as the bottom margin between the RSS feed images and the text.