Seems to me, the only difference is while you are farming heroics, you get to run an old raid once a week with the way you are suggesting. You can do that now though, right? The system still allows you to run tiers progressively. The only difference really is that others aren't forced to do it with you. (Edit: And this sounds like what it is like if you are on or ahead of the curve and not playing catch up at all). Also, with the way they are changing valor and justice, who knows just how it will work for Mists.
now we have to run heroics to buy gear with valor, run the normal modes.. then run the same damn bosses over and over again on heroic... that isnt fun..