Leave the promo-link space to use different blocks if it required. At this moment this space it is just to insert a link but there is not an option to insert anything else. I was wondering if we could use different components in this area, like html blocks.
Thank you for the idea! I understand the request. Unfortunately, Masthead is a block (not a chain) so it's doesn't work to bring a block-within-a-block the way a Navigation chain does. Right now this isn't on our immediate roadmap, but I will put it as "Future Consideration" status to see if it generates interest. If the meantime, you can fork the block and change it to do what you need. Here is some documentation on ALC on how to fork a block.