One problem with implicit IDs is that they change when the heading changes. If you’re serious about cross-referencing in large documents, you want to guard against this, otherwise you’re spending your time updating links when you change headings. There are many reasons you might want to change the heading but keep the section same - to make it more informative, replace a word with another, etc.
So the best option of the options in the above vote is to support explicit IDs which may displace implicit IDs, or don’t specify implicit IDs in the spec at all and then systems which already generate implicit IDs will have to choose to displace the implicit ID with explicitly specified ID, when specified.