Eve, the only reason to "downgrade" (wow, this word sounds horrible!) is cause you are breaking a relationship......and i think there is no reason to move from lover to friends or, more worst!, from spose to lover! it will mean the magic is ended and, honestly, i prefer a complete break!
Well I didn't "downgrade" anybody by myself ( just mentioning the possibility to do ), but I was, once from Lover to Friend, with an explanation of why. And it was fine by me.
I mean, we sometime make mistakes ( in fact I do ) about relationship, or the feeling a relationship may be. So with explanations to the person, it is quite easier with the new system than previously, to update a relationship without cutting all the link.
So, even I too dislike the word "downgrade" ( But I was not able to find a better one ), I maybe , a day, use this possibility, not without chat and explanations of course, just because sometime a once Lover reveal only to be a Friend.
I also agree you, than in case of rupture, I prefer a complete break ... But I don't agree you : there is many reason to update relations...
Please accept my best humbly regards