Is it possible to view a friend's collection?
A little old question, but yes you can, via your friends profile, if he has set his collection to public.
Another thing that I would like to see: Check how many copies of a card I've added to my decks and compare it to the number of cards in my collection.
The background for this feature is the following: in my playgroup we agreed that we can use proxies for our commander decks, as long as the card is in the collection at least once. This made me usually print half the deck and then slowly replacing it with originals (at least for the affordable ones). But if I want to know, which cards I'm missing, I have to check all my decks by hand.