Yes, it used to be so, until very recently. Either Duolingo has adopted the new spelling, or chose to keep this strictly BP. I think it's the latter. If you're interestd in EP, here' a dictionary, that even has an option of displaying the old and the new spelling: http://www.priberam.pt/DLPO/ ("Acordo ortográfico" checkbox)
Actually, now that I think of it, this is not one of those words, because the first "c" is not silent. It sounds like "sék-são", so this is strictly BP, as I thought. Luis (the bloke that devised all of this) said something about it in a discussion. They have done it differenlty with Spanish.
As far as the site itself is concerned, I know they are. If you mean the language content, I think they are, but haven't seen firsthand the improvements.
I don't think you can, the closest thing you get is the "Recommended" tab in the "Follow people" menu, but I can't fathom what the criteria for that might be.