Recent Changes:
Cyclonic Rift moved to SB
2-4 Dawn Charm kept in main. It's just too useful, especially against burn to the face. It's the best 2-mana fog I think there is (Batwing Brume is fun too against those who attack wide with tokens or whatever). Others, like Defend the Hearth, just don't make the cut anymore, since they only prevent damage to me, and I have Planeswalkers to protect now.
So, Defend the Hearth out, Batwing Brume in - it's just plain better.
Nissa, Vastwood Seer
Flip out. Doing things with lands is great, but it's otherwise not very useful for the overall control strategy.
I'm undecided about what counterspell to keep in mainboard: I love Dissolve. It's a hard counter; it scries. Mana Leaks and Remands are available at cheaper cost, but I don't think I need counterspells as importantly early game. Modern is fast, but most strategies are still aggro, and there are plenty of ways for me to deal with creatures until I have enough mana available to Dissolve whenever I want.
Also undecided about whether to mainboard at least a single Riot Control. It's a 3-mana fog that really only has value if opponent has a lot of creatures . .
[EDIT: Just remembered that Riot Control prevents all damage, not just combat damage. It definitely deserves at least 1 main and 2-3 on the side as more protection against burn.]
I took Jace, Architect of Thought out, but he might go back in - at least a one-of in mainboard. It's a solid 4-cost 'walker.
Whelming Wave might move to sideboard. There are already a few other remove-all-creatures options. I do like that it is a relatively cheap way to not only clear away the opponent's army (perhaps after using Riot Control the previous turn), but also return my own Torrential Gearhulk to hand for more shenanigans later.
If Sorin, Lord of Innistrad weren't so damned-good, this would likely be a 4-color deck. The only other thing left in this current version that still has a black mana symbol on it is Batwing Brume . .
(Vraska the Unseen and Ob Nixilis Reignited have found their way into this deck from time-to-time though.)
Devastation Tide had to come out. It's so useful for getting rid of pesky artifacts and enchantments, and there could be some good reason to want to bounce all my own PWs, but it's not instant, so it doesn't make a good save-my-friends rescue card, and the timing is rarely right to take advantage of the miracle cost. .
Reduce to Dreams is now in the SB for those non-creature threats.
Mind Control came out. It might find a home in the side if it seems like there are enough good opposing creatures to steal in the meta. Right now, it is too expensive for such a limited effect.
Elixir of Immortality has been added to SB as a maybe-I'll-draw it against Mill insurance card, since I have no other protections against that. Gaining 5 life is always welcome, especially if I run out of answers to direct burn, and late-game being able to restock my library with fogs and counterspells could save my bacon.
Frozen Aether was in mainboard, then sideboard, then - meh - It's annoying for the opponent, but I'd rather do other things with 4 mana.
Finally, recently added at the top of the curve is Deploy the Gatewatch. With only 8 Planeswalkers in the deck, it isn't likely to catch 2 at the same time, but being able to dig 7 deep for an Elspeth, Sun's Champion or Ajani Vengeant can be a game changer.
Oh, and the land base is still in constant flux. I'm still digging through my collection for the best dual lands to use. I know I have a couple Sacred Foundry somewhere. I always wish I had them in there when there's an opportunity to Windswept Heath for it when I'm ready to drop Ajani, or if I need that second red for Anger of the Gods. I always seem to have enough green or white available to fog when needed, and it seems like there is enough blue by the time I'm ready to Dissolve something, or play one of the many big blue things.