It seems that the <content> element is being deprecated in favor of a new <slot> element in the Web components spec. Would be good to keep tabs on it.
is the <slot> element related to the slot attribute in any way or would that be a separate request? I'm not seeing it in caniuse, but it's possible I'm searching for the wrong thing OR that it's already widely supported and I am just out of touch...
is the
<slot>element related to the slot attribute in any way or would that be a separate request?
They're linked - see How to Use HTML template & slot With Shadow DOM - although the Shadow DOM has very poor (native) browser support so far.
Available at https://caniuse.com/#feat=mdn-html_elements_slot & https://caniuse.com/#feat=mdn-api_htmlslotelement