Off the top, if your primary goal is knights + tree herders + elementals, have you considered Order of the Green Lady (no herders but water elementals, including formation, as well as earth) or Sylvan Kin (no water elementals but forest shamblers)? Both have strong knights, which Nature does not, and access to high def (earth for Order, herders for Kin).
As for the scouting elemental concept, I have a Herd army that’s basically a Verdant Nature army but with a bunch of spear goat regiments and friends (2x herders + 3x forest shambler hordes is the scouting block). It’s … not great? Partially because shambler hordes are pretty mediocre. They don’t really grind and they certainly don’t punch hard. Herders, however, are amazing, tho I really look forward to when their surge becomes optional to save points
All my games with the army have been reported over at blood-fire.com if you’re interested in anecdotal research (click The Hallow on the right for those reports).
Shambler regiments, however, are some of the best thicc chaff in the game, especially as scout helps them with scenario duties, while scouting a horde seems to get them killed faster most times.
I think knights + tough elementals + fast chaff + flying hammers (beasts or greater air elementals) + bane / heal support is a great concept, that Nature doesn’t quite have the first component of. That said, Riverbourne Naiad Wyrmriders are the first time wyrmriders have looked interesting, they might serve as your cav hammer? If you’ve got minis that you like for that, fairly monstrous for ‘green knights’.
EDIT: Here’s me messing around with Nature to make a (large) cav + De 6 + elementals + support:
Forces of Nature
Riverbourne Naiad Wyrmriders (Horde)
Riverbourne Naiad Wyrmriders (Horde)
Water Elementals (Horde)
Earth Elementals (Horde)
Forest Shamblers (Regiment)
Forest Shamblers (Regiment)
Pegasus
Tree Herder - Upgrade to Wiltfather [1]
Gladewalker Druid - Lute of Insatiable Darkness, Surge (8), Ring of Harmony [1]
Unicorn - Replace Heal (5) with Lightning Bolt (5), Upgrade with Wings
Unicorn - Replace Heal (5) with Lightning Bolt (5), Upgrade with Wings
Total Unit Strength: 20
Total Units: 11
Target Points: 1990
It’s very much the good stuff from Nature (except for greater air elementals) plus wyrms. Not sure if it scratches that itch you’re after, or if it’s super great in game, but theoretically it has legs - and wings!