Here are some potential un-bans:
1. Thran dynamo: here we have a very powerful card. 4 mana to jump you straight to 8, not to mention later in the game when you can play it and lose only 1 mana. However, i think it's safe to try. i feel our meta is becoming more and more hostile to artifacts as it should. Everyone runs them and they have been running around unanswered for too long. I have a couple basic criteria for determining whether a card should be banned. 1. Is it an auto include in any deck that can run it if that deck wants to be optimal. 2. Does it invalidate many or all other strategies, aka, does it warp the meta around it. 3. Are there no easy answers, and, how soon must it be answered before the game is over. Ramp has always been, and likely always will be a strategy. Much like drawing extra cards, playing extra mana bends the rules of magic and allows you to do things no one else is capable of doing. Thran dynamo didn't break either 1 or 3 in my eyes and the only way to see if #2 falls is to give it a go.
2. Mystical Tutor - this card was only added to the list because at the time we felt time stretch might actually be over powered. time stretch has not looked bad as your decks have become more and more tuned. I feel each deck still has room for even further improvement as we go further. the other reason is, why is this even a real option. Lots of other cards tutor time stretch, especially if we look outside of blue. In hindsight, if mystical tutor breaks time stretch then i think time stretch is the real problem. 3. Worn Powerstone - like thran, i think it's a perfectly safe card to try. I feel ramp is feared because the archtype is more explored, and the decks that play it, more tuned. I have yet to see a true aggro deck that's tuned to beat ramp. People call me a "spike" because i tune my decks. To me, this is truly the biggest part of magic: making a focused, consistent deck that has a game plan. Think about what you're deck is trying to accomplish. When you look at your deck, imagine what the board will look like as you win the game. How do i win? This will make looking at cards critically (in the interest of your plan) a lot easier.
Just my thoughts on the banned list as is