I've even read the suggestion (not here) that
maybe Tolkien, late in life, 'intended' to have Glorfindel fight a notable demon... but something that is not a Balrog specifically. Like, perhaps a notable Maia in orc form.
The suggestion was based on the late Glorfindel texts, because Tolkien used 'demon' throughout instead of Balrog, and in at least one instance, for some reason changed the word Balrog to demon. I must admit I have no great answer as to why Tolkien would revise the word
Balrog to
demon -- but also no great answer as to why, if indeed he meant to revise the encounter in this way, he wasn't more explicit about it (though granted these are still, to him, his private papers).
Anyway, I don't buy it myself
but I thought it was interesting.