This is a rough sketch or outline of a deck I think could be strong in a post-rotation metagame. The idea is very straightforward: play the biggest, best creatures, be able to block any small stuff, and smash face. We get to play a lot of colors because of Aether Hub, basic-land-searchers (Attune with Aether, Traverse the Ulvenwald, Evolving Wilds), and the new Servant of the Conduit. We want to play a lot of colors mostly for Woodland Wanderer.
Tamiyo is tremendous with both the aforementioned Woodland Wanderer as well as Sylvan Advocate. It's also just a straight-up good card, of course. Verdurous Gearhulk makes sure that we have the biggest creatures around and can push through big damage.
There are a lot of things I'm a bit less sure on with the deck. What should the 4th color be? Red gives us access to Radiant Flames, plus a few other cards. Should we go up to the 4th Tamiyo? How good is the new Nissa here? How many 2 drops do we want - Servant of the Conduit and Sylvan Advocate seem like locks, and here I've supplemented 2 Lambholt Pacifist, but this probably isn't the best Lambholt deck ever - we're all sorcery speed, which makes it hard to flip, for instance. It's possible we want more or less, or we might want Selfless Spirits instead - one of our biggest weaknesses is to Wraths (which really look to be white now).
The 3 drop slot is another big question - there are a lot of options here, between Kambal, Tracker, Fairgrounds Warden, Spell Queller, Thalia, Reflector Mage... and that's only the creatures. Maybe some removal, card draw, planeswalkers also could fit in that slot.
So there are a lot of ways the deck can go. But one thing I want to touch on is of course the mana base. If we count Aether Hub as a source of all colors (which is a little bit precipitous), then our lands give us 18 sources of green (13 of which are untapped), with 10 land-based sources of each other color. On top of that, we have the 6 spell-based basic-searchers, which gets us to 16 sources of each of those colors contingent on having a Green mana, plus the 4 Servants of the Conduit. This looks like a lot - 20 sources for the splash colors certainly is - but of course in reality we're counting all the land searchers and Aether Hub can't reliably be sources of 4 different colors. I think this should be sufficient to be ok, but I'd definitely want to do some testing (or at least simulation) to make sure we're actually hitting our mana reasonably, and that we aren't over-fixing. If we could trim a land-searcher or two, that would be tremendous, especially because A) we're currently sitting on 32 mana sources (counting the 1 CMC searchers and the mana dorks), and B) counting the searchers as tap-lands, we have fully 12 of those. I would be remiss if I didn't note that while we can definitely tweak the mana a bit, it's pretty hard to get to double of any non-green color reliably (I think), though you probably could if you really wanted to (though it would mean some sacrifices).
In terms of the sideboard, this is really thrown together quickly. Selfless Spirits are protection against sweepers (reasonable against other ground decks). Kambal seems good against burn, as does the Stomper. Negate is good against control and burn. And there are a handful of other cards against control. Frankly the sideboard is probably really bad, and I at least want to consider some Naturalize effects, but mostly you need to have some expectation of a metagame before you can properly build a 'board.