In /ezpublish/vendor/ezsystems/ezpublish-kernel/eZ/Publish/Core/FieldType/XmlText/Input/Resources/schemas/ezxml.xsd
we can see that "object_remote_id" in "link" tags are allowed.

Unfortunately, in
/ezpublish/vendor/ezsystems/ezpublish-kernel/eZ/Publish/Core/FieldType/XmlText/Converter/EzLinkToHtml5.php
we can see that this attribute is not handled at all.

steps to reproduce:

. Using the API publish some content that will set the following into a XmlBlock field

<<< EOX
<?xml version='1.0' encoding='utf-8'?>
<section>
<paragraph>Link with node_id: <embed view='embed' size='medium' node_id='114'/></paragraph>
<paragraph>Link with object_remote_id: <embed view='embed' size='medium' object_remote_id='41fa1463f99fc75f720d992ab1a3587f'/></paragraph>
</section>
EOX;

(adapt node_id and object_remote_id to match some content in your database)
. View the page in through a twig based rendering (using ez_render_field)
(small_folder.html.twig from DemoBundle will do just fine)
. You'll notice that only the first link (node_id) is actually rendered. The link with object_remote_id will not be showed.