Because I love to theorycraft, I constructed a few possible Pomace progressions using herb lists from WoW's main site.
The first grouping I went with the basic, "In groupings of 4" criteria I've seen with the other pomaces and read from information posted in the beta forums. It makes alot of sense this way, but I think it's too simplistic. Besides, I can imagine blizzard making it painfully hard to level from 310-375 like blacksmithing was (hopefully they don't though).
Peacebloom
Silverleaf
Earthroot
Mageroyal
Briarthorn
Swifthistle*
Stranglekelp
Bruiseweed
Wild Steelbloom
Grave Moss
Kingsblood
Liferoot
Fadeleaf
Goldthorn
Khadgar's Whisker
Wintersbite
Firebloom 205 open
Purple Lotus 210 near ruins
Arthas' Tears 220 open
Sungrass 230 open
Blindweed 235 near water
Ghost Mushroom 245 caves
Gromsblood 250 open
Golden Sansam 260 open
Dreamfoil 270 open
Mountain Silversage 280 cliffs
Plaguebloom 285 open
Icecap 290 cliffs
Felweed 300 open
Dreaming Glory 315 cliffs
Terocone 325 near trees
Ragveil 325 open
Flame Cap 335 open
Ancient Lichen 340 dungeon
Netherbloom 350 open
Nightmare Vine 365 open
Mana Thistle 375 open
Like I said, this is a rather simplistic approach to it. I left intact some of the herbalism harvesting rating reqs to demonstrate how for the most part the herbs share some kind of similarity. I left Mana Thistle detached because most final throws in a profession require a strange top tier resource. Things like wildvine, heart of the wild, and fel lotus were omitted based on their scarcity. If anything, I think the final 25 points will be leveled by combining inks (possibly) or using primals in the process.
My second school of though is that future pomaces will be categorized based on mill ratings. This has been removed from a Beta posting (if there are inaccuracies with my ratings vs El's ratings, I apologize ahead of time).
Groupings based on Mill rating:
-Gromsblood 175
-Ghost Mushroom 175
-Blindweed 175
-Sungrass 175
-Arthas' Tears 175
-Purple Lotus 175
-Firebloom 175
Icecap 225
-Plaguebloom 225
-Mountain Silversage 225
-Dreamfoil 225
-Golden Sansam 225
Mana Thistle 275
-Nightmare Vine 275
-Netherbloom 275
-Ancient Lichen 275
-Ragveil 275
-Terocone 275
I assume this might be the more likely of the two, especially considering that the low level pomaces are grouped by herbs with the same mill rating.
Like I said prior, this is just conjecture. Stock at your own risk :)