As this is purely speculation, please feel free to present this faction as a definite, absolute certainty for inclusion going forward on these forums!
As Red Dox shared this map:

It is clearly necessary to flesh out the units and the faction for what
might possibly is
likely certain to be a DLC race in game 3! Unfortunately GW neglected to include the faction in the 8th edition army books; an oversight on their part. Nevertheless the great news is that there are fantastic depictions of many of their units and infantry out there. Please feel free to suggest any units and characters I might have missed.
Infantry:Amateur 'Jacks
The one handed axe menSturdy infantry, no armour so relatively fast, could include a shield wielding variant.

Throwing axesShort ranged, armour piercing, no armour, relatively fast but limited ammunition. Decent melee combatants.

The two handed axe menArmour piercing variant. No shields and susceptible to ranged attacks. Strong in melee and relatively fast. Also very cheap as, like the one handed variety, they do not wear armour.

Weapon team - the two man sawArmour piercing and anti-large. Slower moving than the regular infantry.

Super-heavy infantryArmour piercing. Anti-large. Causes terror. These are the shock troops of the Lumbrian army and are quite capable of cutting through even the most elite troops of other factions. They wear light armour but are slow moving (health and safety!)

Chariots:The faction does not employ cavalry but there are several chariot options available to them.
Light chariotArmoured, skirmisher chariots, fast.

Heavy chariot
Shock unit, powerful charge, armoured

Super heavy chariot with special weaponI managed to find an original minature of this one!
Armoured, armour piercing, powerful charge, special weapon

Heroes and Lords:I think that there may be many more to add in this area.
Veiled AssassinHero, lurks within the enemy army, adept at taking down individual unsuspecting enemies (duelist)

Wooden ManA carved effigy of a man, inhabited by the spirit of a wanderer lost within the forest. Missile resistant, armoured, susceptible to flame
"For the matter to be laid to rest, you must destroy that which keeps you alive and be immortal no longer" - Deionarra's prophecy (I had to get something from Planescape: Torment in there!)

Paul Bun'onion (and his Babe)Faction leader and Legendary Lord
The miniature below is from the 3rd Edition army book I believe
Giant, armour piercing, Melee expert, Bad breath (oniony). Think Skarnik and Gobbla... just massive (and not a spellcaster).

Faction traits:Bonus damage against treemen etc.
Use fire
And of course:
Have cheerful ditties

Comments
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3 · Disagree Agree- Report
6 · Disagree AgreeFrikking TIMBERRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
Top #3 Leaderboard on Warhammer Totalwar.
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2 · Disagree Agree- Report
0 · Disagree AgreeBefore they realised sartosa lumberjacks would inevitebly overlap with lumbrian ones and must be changed.
Do you think they changed it because of our cries, no it was a small teaser for lumbria.
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2 · Disagree AgreeTomb Kings
The Empire
"Surrender and serve me in life, or die and slave for me in death." - Vlad von Carstein
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0 · Disagree Agree- Report
4 · Disagree Agree- Report
2 · Disagree AgreeMORE likely then araby....
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0 · Disagree AgreeIn treeless regions like Nehekhara or the Badlands they should get huge attrition, because they have nothing to chop so they start chopping each other’s heads.
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0 · Disagree AgreeWe need lumberjacks's paradise. Grimbeorn should be Legendary Lord for them!
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0 · Disagree Agree- Report
0 · Disagree Agreehttps://steamcommunity.com/sharedfiles/filedetails/?id=1559010020
Bring back proper naval battles CA!!!
Me when I see a LL character implemented as a LH.
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1 · Disagree AgreeAnd, since naturally when thinking about possible critters for a faction based on a real-world culture it is imperative to incorporate every creature from that culture's mythology regardless of whether those creatures are friendly or hostile to that culture, we would naturally look to include as many of these as possible.
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2 · Disagree Agree- Report
0 · Disagree Agree- Report
1 · Disagree Agree- Report
0 · Disagree AgreeThe Fearsome Critters feel more like opponents to be faced within the artifact quests.
The roster is starting to come along quite nicely. I don't think that @CA can ignore this faction for long. Pre-order bonus maybe?
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0 · Disagree Agree